Integer Division

[Anjanesh Lekshminarayanan]

>>> a = 1
>>> b = 25
>>> a / b
0
>>> float(a) / b
0.040001
>>>

>>> from __future__ import division
>>> a = 1
>>> b = 25
>>> a / b
0.040001
>>>

In what simple way can I get just 0.04 ?

-- 
Anjanesh Lekshmnarayanan
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Re: Integer Division

[Chris Rebert]

On Fri, Jun 19, 2009 at 12:22 AM, Anjanesh
Lekshminarayanan wrote:
 a = 1
 b = 25
 a / b
> 0
 float(a) / b
> 0.040001

>
 from __future__ import division
 a = 1
 b = 25
 a / b
> 0.040001

>
> In what simple way can I get just 0.04 ?

Note that what you are shown is the repr() of the float rather than
the str() of the float. The repr() value is what the number truly is
in binary, but str() applies more sensible rounding.

Example (remember that print() does an implicit str()):
>>> from __future__ import division
>>> print(1/25)
0.04
>>> repr(1/25)
0.040001
>>>

Alternatively, you can use the decimal arithmetic library:
>>> from decimal import Decimal
>>> Decimal(1)/Decimal(25)
Decimal('0.04')
>>>

Cheers,
Chris
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Re: Newbie queue question

[Jure Erznožnik]

I've done some further testing on the subject:

I also added some calculations in the main loop to see what effect
they would have on speed. Of course, I also added the same
calculations to the single threaded functions.
They were simple summary functions, like average, sum, etc. Almost no
interaction with the buffers was added, just retrieval of a single
field's value.

Single threaded, the calculations added another 4.3 seconds to the
processing time (~18%)
MultiThreaded, they added 1.8 seconds. CPU usage remained below 100%
of one core at all times. Made me check the process affinity.

I know the main thread uses way less CPU than DBF reading thread (4
secs vs 22 secs).
So I think adding these calculations should have but a minimal impact
on threaded execution time.

Instead, the execution time increases!!!
I'm beginning to think that Python's memory management / functions
introduce quite a significant overhead for threading.

I think I'll just write this program in one of the compilers today to
verify just how stupid I've become.
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Re: walking a directory with very many files

[Mike Kazantsev]

On Fri, 19 Jun 2009 17:53:40 +1200
Lawrence D'Oliveiro  wrote:

> In message <20090618081423.2e035...@coercion>, Mike Kazantsev wrote:
> 
> > On Thu, 18 Jun 2009 10:33:49 +1200
> > Lawrence D'Oliveiro  wrote:
> > 
> >> In message <20090617214535.10866...@coercion>, Mike Kazantsev
> >> wrote:
> >> 
> >>> On Wed, 17 Jun 2009 23:04:37 +1200
> >>> Lawrence D'Oliveiro  wrote:
> >>> 
>  In message <20090617142431.2b25f...@malediction>, Mike Kazantsev
>  wrote:
>  
> > On Wed, 17 Jun 2009 17:53:33 +1200
> > Lawrence D'Oliveiro  wrote:
> > 
> >>> Why not use hex representation of md5/sha1-hashed id as a
> >>> path, arranging them like /path/f/9/e/95ea4926a4 ?
> >>> 
> >>> That way, you won't have to deal with many-files-in-path
> >>> problem ...
> >> 
> >> Why is that a problem?
> > 
> > So you can os.listdir them?
>  
>  Why should you have a problem os.listdir'ing lots of files?
> >>> 
> >>> I shouldn't, and I don't ;)
> >> 
> >> Then why did you suggest that there was a problem being able to
> >> os.listdir them?
> > 
> > I didn't, OP did ...
> 
> Then why did you reply to my question "Why is that a problem?" with
> "So that you can os.listdir them?", if you didn't think there was a
> problem (see above)?

Why do you think that if I didn't suggest there is a problem, I think
there is no problem?

I do think there might be such a problem and even I may have to face it
someday. So, out of sheer curiosity how more rediculous this topic can
be I'll try to rephrase and extend what I wrote in the first place:


Why would you want to listdir them?
I can imagine at least one simple scenario: you had some nasty crash
and you want to check that every file has corresponding, valid db
record.

What's the problem with listdir if there's 10^x of them?
Well, imagine that db record also holds file modification time (say,
the files are some kind of cache), so not only you need to compare
listdir results with db, but also do os.stat on every file and some
filesystems will do it very slowly with so many of them in one place.


Now, I think I made this point in the first answer, no?

Of course you can make it more rediculous by your
I-can-talk-away-any-problem-I-can't-see-or-solve approach by asking "why
would you want to use such filesystems?", "why do you have to use
FreeBSD?", "why do you have to work for such employer?", "why do you
have to eat?" etc, but you know, sometimes it's easier and better for
the project/work just to solve it, than talk everyone else away from it
just because you don't like otherwise acceptable solution.

-- 
Mike Kazantsev // fraggod.net


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MailingLogger 3.3.0 Released!

[Chris Withers]

I'm pleased to announce a new release of Mailinglogger.

Mailinglogger provides two handlers for the standard python
logging framework that enable log entries to be emailed either as the
entries are logged or as a summary at the end of the running process.

The handlers have the following features:

- customisable and dynamic subject lines for emails sent

- emails sent with an X-Mailer header for easy filtering

- flood protection to ensure the number of emails sent is not excessive

- support for SMTP servers that require authentication

- fully documented and tested

In addition, extra support is provided for configuring the handlers when
using ZConfig, Zope 2 or Zope 3.

The latest releases of ZConfig, in particular, provide a great way to 
configure the python logging framework without having to resort to the 
appalling .ini-based configuration stuff:


>>> from ZConfig import configureLoggers
>>> configureLoggers('''
... 
...level INFO
...
...   PATH STDOUT
...   format %(levelname)s %(name)s %(message)s
...
... 
... ''')

This release of MailingLogger adds the ability to use %(levelname)s in 
subject-line formatting for SummarisingLoggers to include the highest 
level logged.


For more information, please see:
http://www.simplistix.co.uk/software/python/mailinglogger
or
http://pypi.python.org/pypi/mailinglogger

cheers,

Chris

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Re: Integer Division

[Mark Dickinson]

On Jun 19, 8:22 am, Anjanesh Lekshminarayanan 
wrote:
> >>> a = 1
> >>> b = 25
> >>> a / b
> 0
> >>> float(a) / b
>
> 0.040001

Python typically stores floats in binary, not decimal.  The
value 0.04 isn't exactly representable in binary, so the
division float(1)/25 can't produce 0.04:  what you get instead
is a very good approximation to 0.04.  That's why you're
seeing what you're seeing above.  Note that 0.0400...001 is
*also* just an approximation to the actual value stored, but
it's a better approximation than 0.04.  The exact value stored
is (probably, assuming your machine is typical):

0.04832667268468867405317723751068115234375

or, if you prefer, it's:

5764607523034235/144115188075855872

> In what simple way can I get just 0.04 ?

The answer to that depends on what you want and why you
want it.  Do you want a string or a number?  And if you
want a number, does it have to be *exactly* 0.04, or
can your application cope with a tiny error?

If you're trying to get a string and just want things
to look nice, use str() instead of repr(),
or display the value using print.  If you want more control
over the number of digits displayed, use Python's string
formatting:  e.g., in Python 2.6:

>>> format(0.04, '.3f')  # format with 3 places after the point
'0.040'

See the following for more information on format:

  http://docs.python.org/library/string.html#formatstrings

If you're after the number and you *really* need to
be able to manipulate the *exact* value 0.04 in Python
(e.g., because you're doing financial work), you're probably
better off using the Decimal module:

  http://docs.python.org/library/decimal.html

See also:

  http://docs.python.org/tutorial/floatingpoint.html

Mark
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Slow wxPyhon on Vista?

[Martin Schöön]

Hello there,

this might be my first post here and it is slightly off
topic since it is not about something I am developing.

At work use a nifty little program called Task Coach.
It helps me keep track of what I spend time on.

Here is my problem. When I use it on a Vista box its
user interface is very, very slow when it comes to
some but not all operations. On any other Windows
version it reacts instantaneously. I have not tried
Task Coach on Linux or Solaris (yet).

Is this how wxPython or Python works on Vista in
general or is this the result of some local oddity on my
employer's Vista configuration?

TIA,

/Martin
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Re: Newbie queue question

[Jure Erznožnik]

Digging further, I found this:
http://www.oreillynet.com/onlamp/blog/2005/10/does_python_have_a_concurrency.html

Looking up on this info, I found this:
http://docs.python.org/c-api/init.html#thread-state-and-the-global-interpreter-lock

If this is correct, no amount of threading would ever help in Python
since only one core / CPU could *by design* ever be utilized. Except
for the code that accesses *no* functions / memory at all.

This does seem to be a bit harsh though.
I'm now writing a simple test program to verify this. Multiple data-
independed threads just so I can see if more than one core can at all
be utilized.

:(
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Re: Newbie queue question

[Tim Harig]

On 2009-06-19, =?windows-1252?Q?Jure_Erzno=9Enik?=  
wrote:
> If this is correct, no amount of threading would ever help in Python
> since only one core / CPU could *by design* ever be utilized. Except
> for the code that accesses *no* functions / memory at all.

Don't multithread...multiprocess.  By running multiple python instances,
the operating system handles the processor scheduling for each so that you
can use all available CPUs/cores.  It also tends to make debugging easier.
It does create more overhead -- significantly more on some OSs.
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Re: Help: Group based synchronize decorator

[Piet van Oostrum]

> Vishal Shetye  (VS) wrote:

>VS> I want to synchronize calls using rw locks per 'group' and my 
>implementation is similar to
>VS> http://code.activestate.com/recipes/465057/
>VS> except that I have my own Lock implementation.

>VS> All my synchronized functions take 'whatGroup' as param. My lock considers 
>'group' while deciding on granting locks through acquire.

>VS> What I could come up with is:
>VS> - decorator knows(assumes) first param to decorated functions is always 
>'whatGroup'
>VS> - decorator passes this 'whatGroup' argument to my lock which is used in 
>acquire logic.

>VS> Is it ok to make such assumptions in decorator?

As long as you make sure that all decorated functions indeed adhere to
that assumption there is nothing wrong with it.
-- 
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URL: http://pietvanoostrum.com [PGP 8DAE142BE17999C4]
Private email: p...@vanoostrum.org
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Re: Once again, comparison wxpython with PyQt

[Jeremy Sanders]

Hans Müller wrote:

> Thanks for all your informative replies.
> 
> If I understand you right, for a commercial, closed source program I
> only need a commercial PyQt license for ~ 500€ ?

Why not ask the guys at riverbankcomputing?
 http://www.riverbankcomputing.co.uk/commercial/pyqt

This page
 http://www.riverbankcomputing.co.uk/software/pyqt/license

Says "The commercial version of PyQt can be used with both the commercial 
and LGPL versions of Qt."

> As far as I know I also need a Qt Licenses which is ~3500€ per OS.

Not true, now Qt is licensed under the LGPL.

You have to abide by the LGPL, however, which means that the user has to be 
able to relink a modified form of the library, Qt, with your application 
should they wish. You should check whether the LGPL is appropriate for the 
way you want to ship your program.

Jeremy

-- 
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http://www.jeremysanders.net/

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Re: Tutorial on working with Excel files in Python (without COM and cross platform!) at EuroPython 2009

[Piet van Oostrum]

> John Machin  (JM) wrote:

>JM> [1] No kidding: http://www.google.com/patents/about?id=QMwnEBAJ

Apart from these patents probably being silly, why don't they just write
the code in Python? :=)
-- 
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URL: http://pietvanoostrum.com [PGP 8DAE142BE17999C4]
Private email: p...@vanoostrum.org
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ErrorHandler 1.0.0 Released!

[Chris Withers]

I'm pleased to finally get around to announcing the release of ErrorHandler.

This is a handler for the python standard logging framework that can
be used to tell whether messages have been logged at or above a
certain level.

This can be useful when wanting to ensure that no errors have been
logged before committing data back to a database.

Here's an example:

First, you set up the error handler:

>>> from logging import getLogger
>>> from errorhandler import ErrorHandler
>>> logger = getLogger()
>>> e = ErrorHandler()

The handler started off being un-fired:

>>> e.fired
False

Then you do whatever else you need to do, which may involve logging:

>>> logger.info('some information')
>>> e.fired
False

However, if any logging occurs at an error level or above:

>>> logger.error('an error')

Then the error handler becomes fired:

>>> e.fired
True

You use this as a condition to only do certain actions when no errors
have been logged:

>>> if e.fired:
...   print "Not updating files as errors have occurred"
Not updating files as errors have occurred

If your code does work in batches, you may wish to reset the error
handler at the start of each batch:

>>> e.reset()
>>> e.fired
False

For more information, please see:
http://www.simplistix.co.uk/software/python/errorhandler
or
http://pypi.python.org/pypi/errorhandler

cheers,

Chris

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Excel Formulae in Python ;-)

[Chris Withers]

Piet van Oostrum wrote:

John Machin  (JM) wrote:



JM> [1] No kidding: http://www.google.com/patents/about?id=QMwnEBAJ


Apart from these patents probably being silly, why don't they just write
the code in Python? :=)


Would be cool, but there are things like

Resolver One (http://www.resolversystems.com/product/)

and

DiscoveryScript (http://www.xefion.com/en/discoveryscript.html)

...that help.

cheers,

Chris

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Re: CAD file format specifications?

[PoD]

On Thu, 18 Jun 2009 13:39:28 +0200, Anthra Norell wrote:

>  I had a look at Blender. It looks impressive too. It might be an
> alternative to Sketch Up. I'll worry about that later. My immediate need
> is a file conversion utility. A cursory inspection of Blender's menu
> tabs and the various help options didn't turn up a file-conversion
> utility. So, my question is: How do I convert a bunch of
> three-dimensional coordinates defining lines into a file format Sketch
> Up can read (skp, dwg, dxf, 3ds, ddf or dem)?
> 
> Frederic

If you look in the File/Import menu in Blender, you will see all the file 
types which it can load.

The importing is done with python scripts, so if you are going to write a 
converter you might just as well write an import script for Blender.

The raw import script shows how simple it can be.

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Re: A question on scope...

[Bruno Desthuilliers]

MRAB a écrit :

Wells Oliver wrote:


NB : answering the OP (original post didn't show up on c.l.py ???)

In writing out python classes, it seems the 'self' is optional, 


You mean, inside a method ?


meaning that inside a class method,



In Python, a "class method" is a method that operates on the class 
object itself instead of operating on an instance of the class.



"self.foo = bar" has the same 
effect as "foo = bar". Is this right?


It's obviously false, cf MRAB's answer.
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Status of Python threading support (GIL removal)?

[Jure Erznožnik]

See here for introduction:
http://groups.google.si/group/comp.lang.python/browse_thread/thread/370f8a1747f0fb91

Digging through my problem, I discovered Python isn't exactly thread
safe and to solve the issue, there's this Global Interpreter Lock
(GIL) in place.
Effectively, this causes the interpreter to utilize one core when
threading is not used and .95 of a core when threading is utilized.

Is there any work in progess on core Python modules that will
permanently resolve this issue?
Is there any other way to work around the issue aside from forking new
processes or using something else?
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Re: sqlite3, OperationalError: no such column, shouldn't that ne a ProgrammingError?

[Gerhard Häring]

Gabriel Rossetti wrote:
> Hello everyone,
> 
> I get an OperationalError with sqlite3 if I put the wrong column name,
> but shouldn't that be a ProgrammingError instead? I read PEP 249 and it
> says :
> 
> "OperationalError
>Exception raised for errors that are related to the
>database's operation and not necessarily under the control
>of the programmer, e.g. an unexpected disconnect occurs,
>the data source name is not found, a transaction could not
>be processed, a memory allocation error occurred during
>processing, etc.  It must be a subclass of DatabaseError.
>  ProgrammingError
>Exception raised for programming errors, e.g. table not
>found or already exists, syntax error in the SQL
>statement, wrong number of parameters specified, etc.  It
>must be a subclass of DatabaseError.
> "
> 
> and to me it sounds more like a programming error than an operational
> error.

I agree. But I can't help you there.

See _pysqlite_seterror() at
http://oss.itsystementwicklung.de/trac/pysqlite/browser/src/util.c

What I do is map SQLite error codes to DB-API exceptions. And SQLite
reports your error as generic SQLITE_ERROR, which is mapped to
OperationalError.

-- Gerhard

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Re: preferring [] or () in list of error codes?

[Albert van der Horst]

In article ,
>
>
>But practicality beats purity -- there are many scenarios where we make
>compromises in our meaning in order to get correct, efficient code. E.g.
>we use floats, despite them being a poor substitute for the abstract Real
>numbers we mean.
>
>In addition, using a tuple or a list in this context:
>
>if e.message.code in (25401,25402,25408):
>
>is so idiomatic, that using a set in it's place would be distracting.
>Rather that efficiently communicating the programmer's intention, it
>would raise in my mind the question "that's strange, why are they using a
>set there instead of a tuple?".

As a newby I'm really expecting a set here. The only reason my mind
goes in the direction of 3 items is that it makes no sense in
combination with ``in''.  That makes this idiom one that should be killed.

"
point1 = (0,1,0)
point2 = (1,0,0)
point3 = (0,0,1)
for i in (point1,point2, point3):

"  ???

I don't think so.
At least I would do

"
for i in [point1,point2,point3]:
statements
"

But I greatly prefer a set

"
for i in {point1,point2,point3}:
statements
"
Because a set is unorderded, this would convey to the
the compiler that it may evaluate the three statements concurrently.
For a list I expect the guarantee that the statements are
evaluated in order.
For a tuple I don't know what to expect. That alone is sufficient
reason not to use it here.

[Yes I know { } doesn't denote a set. I tried it. I don't
know how to denote a set ... ]

>--
>Steven

Groetjes Albert.

--
-- 
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Economic growth -- being exponential -- ultimately falters.
alb...@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst

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Re: Allocating memory to pass back via ctypes callback function

[Scott]

I think I found the answer to my own question.  Can anyone spot any
issues with the following solution? The application I'm writing will
be hitting these callbacks pretty heavily so I'm nervous about mucking
up the memory management and creating one of those bugs that passes
undetected through testing but nails you in production.

def my_callback(p_cstring):
answer = 'foobar'

address = VENDOR_malloc(len(answer)+1)

cstring = c_char_p.from_address( address )

cstring.value = answer
p_cstring.contents = cstring
return
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Re: Slow wxPyhon on Vista?

[David Lyon]

On Fri, 19 Jun 2009 10:16:39 +0200, martin.sch...@gmail.com (Martin
Schöön) wrote:
> Here is my problem. When I use it on a Vista box its
> user interface is very, very slow when it comes to
> some but not all operations. On any other Windows
> version it reacts instantaneously. I have not tried
> Task Coach on Linux or Solaris (yet).
> 
> Is this how wxPython or Python works on Vista in
> general or is this the result of some local oddity on my
> employer's Vista configuration?

I have encountered the same thing on XP in one instance
on a development box. For some reason, wxpython just
grinds to a halt.

I couldn't solve it and reimaged the O/S... that
fixed it...

David
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Re: Newbie queue question

[Piet van Oostrum]

> Jure Erznožnik  (JE) wrote:

>JE> Digging further, I found this:
>JE> 
>http://www.oreillynet.com/onlamp/blog/2005/10/does_python_have_a_concurrency.html

>JE> Looking up on this info, I found this:
>JE> 
>http://docs.python.org/c-api/init.html#thread-state-and-the-global-interpreter-lock

>JE> If this is correct, no amount of threading would ever help in Python
>JE> since only one core / CPU could *by design* ever be utilized. Except
>JE> for the code that accesses *no* functions / memory at all.

It is not the design of the Python language, but of the Python
implementation. And yes, it will not benefit from more than one core.

You should watch/read this:
  http://blip.tv/file/2232410
  http://www.dabeaz.com/python/GIL.pdf 

-- 
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Re: Integer Division

[Piet van Oostrum]

> Anjanesh Lekshminarayanan  (AL) escribió:

> a = 1
> b = 25
> a / b
>AL> 0
> float(a) / b
>AL> 0.040001
> 

> from __future__ import division
> a = 1
> b = 25
> a / b
>AL> 0.040001
> 

>AL> In what simple way can I get just 0.04 ?

In addition to the answers others have given:

>>> 0.04
0.040001
>>> 

IIRC, Python 3.1 will give 0.04. But this doesn't mean the answer will
be mathematically equal to 0.04, just that it tries to make it less
painful. 
-- 
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Re: Excel Formulae in Python ;-)

[Piet van Oostrum]

> Chris Withers  (CW) wrote:

>CW> Piet van Oostrum wrote:
 John Machin  (JM) wrote:
>>> 
>JM> [1] No kidding: http://www.google.com/patents/about?id=QMwnEBAJ
>>> 
>>> Apart from these patents probably being silly, why don't they just write
>>> the code in Python? :=)

>CW> Would be cool, but there are things like

>CW> Resolver One (http://www.resolversystems.com/product/)

>CW> and

>CW> DiscoveryScript (http://www.xefion.com/en/discoveryscript.html)

>CW> ...that help.

Actually, I meant writing the patent application in Python :=) instead
of this pseudo-exact legalese with goto instructions for the control
flow. 
-- 
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Private email: p...@vanoostrum.org
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Re: Newbie queue question

[Piet van Oostrum]

> Jure Erznožnik  (JE) wrote:

>JE> Digging further, I found this:
>JE> 
>http://www.oreillynet.com/onlamp/blog/2005/10/does_python_have_a_concurrency.html

>JE> Looking up on this info, I found this:
>JE> 
>http://docs.python.org/c-api/init.html#thread-state-and-the-global-interpreter-lock

>JE> If this is correct, no amount of threading would ever help in Python
>JE> since only one core / CPU could *by design* ever be utilized. Except
>JE> for the code that accesses *no* functions / memory at all.

It is not the design of the Python language, but of the *CPython*
implementation. And yes, it will not benefit from more than one core.

You should watch/read this:
  http://blip.tv/file/2232410
  http://www.dabeaz.com/python/GIL.pdf 

-- 
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URL: http://pietvanoostrum.com [PGP 8DAE142BE17999C4]
Private email: p...@vanoostrum.org
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Re: Integer Division

[Dave Angel]

Anjanesh Lekshminarayanan wrote:

a = 1
b = 25
a / b


0
  

float(a) / b


0.040001
  

  

from __future__ import division
a = 1
b = 25
a / b


0.040001
  


In what simple way can I get just 0.04 ?

  
Your subject line says "Integer Division" but you're dealing with 
floats.  IEEE standard float cannot exactly represent 0.04   In fact, no 
binary floating point value of finite precision can get that exact 
value.  So if you really want 0.04, you need to use the decimal 
package.  It's the only way you'll be sure of exactly representing any 
decimal fraction you need.


Let's call  val = float(1)/25If you're using future division (or 
Python 3.x), 1/25 will be exactly the same as val.  In either case, the 
division cannot come out exactly, since there is no such exact float.


On the other hand, some *string* representation of val may not come out 
"exact."  Technically, to represent val in decimal digits may take up to 
59 or so characters.  But the two standard conversions from float to 
string ( float.__str__   and float.__val__ ) do a little rounding 
themselves.  So you can try them, and see that one of them "works."  
(print calls the __str__ method, while the interpreter uses __repr__)


The problem with this is that what "works" for one such val might fail 
for the next.  And these __str__ and __val__ have been implemented 
multiple times, so testing on one Python version will not assure 
consistency on the next.


The issue is that you're counting on two approximations canceling each 
other out.  That'll work in some circumstances, but knowing what they 
are isn't reasonable.


So what do people do?  Simplest is to use a decimal package.  I tried 
back in the early 80's to convince the IEEE committee to include decimal 
float in the standard, but was rejected.  I had implemented (microcoded) 
arithmetic and transcendentals on a machine which offered only decimal 
floating point;  no binary floating point.


Next choice?  Stick to integers, or implied fractions.  For example, if 
dealing with dollars and cents, always calculate and store the value in 
pennies, and only insert the decimal when displaying.


Finally, it's not hard (if you know something about the numbers) to get 
a "pretty" display version for yourself, rounding it as you're 
converting to string.


Note that this affects other aspects of your program, such as 
comparisons between two floats.  If you sum up 100 copies of .01, will 
you get exactly 1.0 ?  I don't know, but in many cases, clearly not.


This is not a new problem.  I read about it in McCracken's Fortran book 
in 1967, where he said to use something on the order of:

if  abs(a-b) < .01 ...

when comparing reals.


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Re: preferring [] or () in list of error codes?

[Ben Finney]

Albert van der Horst  writes:

> But I greatly prefer a set
> 
> "
> for i in {point1,point2,point3}:
> statements
> "

Agreed, for the reasons you cite. I think this idiom can be expected to
become more common and hopefully displace using a tuple literal or list
literal, as the set literal syntax becomes more reliably available on
arbitrary installed Python versions.

> [Yes I know { } doesn't denote a set. I tried it. I don't know how to
> denote a set ... ]

Try it in Python 3 and be prepared to be pleased
http://docs.python.org/3.0/whatsnew/3.0.html#new-syntax>.

-- 
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  `\   Bjelke-Petersen |
_o__)  |
Ben Finney
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Re: generator expression works in shell, NameError in script

[Bruno Desthuilliers]

Emile van Sebille a écrit :

On 6/17/2009 3:54 PM ssc said...

Wow! Didn't expect that kind of instant support. Thank you very much,
I'll give both zip and enumerate a try.

The code I've shown is actually copied pretty straight from a Django
form class, but I didn't want to mention that as not to dilute the
conversation. Don't think it matters, anyway. This is the relevant
excerpt:

from django.forms import Form

class SignupForm(Form):

titles = ['Dr', 'Miss', 'Mr', 'Mrs', 'Ms',]
title_choices   = [(0, '')] + list((titles.index(t)+1, t) for t in
titles)

Now that I look at it again, it seems odd to me to not have the code
e.g. in __init__(...), but just 'class-global'.


And as class is an executable statement, I imagine titles exists in a 
namespace that hasn't yet been completely defined.



Still, that does not seem a reason for titles not to be not defined,
as I do define it just in the line above.


Well, again, titles will exists in the SignupForm namespace once it 
exists, which it doesn't yet when you get to title_choices and want to 
access it. 


The namespace itself is as defined at any point of the class statement's 
body as the local namespace of a function at any given point of the 
function's body. Else decorators (or their alternate pre '@' 
syntactic-sugar version) wouldn't work.



FWIW, the following code works JustFine(tm):

br...@bruno:~$ python
Python 2.5.2 (r252:60911, Oct  5 2008, 19:24:49)
[GCC 4.3.2] on linux2
>>> class Foo(object):
... bar = ['a', 'b', 'c']
... baaz = list(enumerate(bar))

as well as this one:

>>> class Foo(object):
... bar = ['a', 'b', 'c']
... baaz = [(bar.index(t)+1, t) for t in bar]

and this one:

>>> class Foo(object):
... bar = ['a', 'b', 'c']
... baaz = list((b, b) for b in bar)



but it indeed looks like using bar.index *in a generator expression* 
fails (at least in 2.5.2) :


 >>> class Foo(object):
... bar = ['a', 'b', 'c']
... baaz = list((bar.index(b), b) for b in bar)
...
Traceback (most recent call last):
  File "", line 1, in 
  File "", line 3, in Foo
  File "", line 3, in 
NameError: global name 'bar' is not defined


Looks like a bug to me :-/

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Decorator question (how to test if decorated function is in a class)

[Martin P. Hellwig]

Hi all,

I have been trying out to wrap my mind around the advantages of 
decorators and thought I found a use in one of my experiments. (see code 
after my sig).


Although it works, I think it should be able to do it better.
My particular problem is that I want to remove an argument (say always 
the first one) when the decorated function is called.


However if the function is defined in a class the first argument is self 
and thus the second argument should be removed.


Since I like to have a more general DRY approach I want to test if the 
decorated function is defined in a class or not thus knowing that the 
first argument is self and must be preserved.


I tried different approaches but all didn't work and looked very 
unpythonic (looking at the attributes, descriptors namespaces, id() of 
the function, the first argument and the decorator itself).


So is there a way to find out if the first argument is 'self' without 
making a false positive if the first argument is a class instance passed 
to a function?


--
MPH
http://blog.dcuktec.com
'If consumed, best digested with added seasoning to own preference.'

code:
class Decorator(object):
"When used as Decorator(argument) returns a decorator"
def __init__(self, key):
self.key = key

def __call__(self, function):
"Return a decorator"
def decorator(*arg_tuple, **arg_dict):
"The decorator test if the arguments contain a valid key"
if arg_tuple[0] == self.key:
# This means it is a simple function, so check and strip it
arg_list = arg_tuple[1::]
return(function(*arg_list, **arg_dict))
elif arg_tuple[1] == self.key:
# This means it is a class method, check it,
# strip (but retain self)
arg_list = arg_tuple
arg_list = arg_list[0:1] + arg_list[2::]
return(function(*arg_list, **arg_dict))
else:
# The key was invalid
return('invalid')

return(decorator)


class Test(object):
@Decorator('key')
def test(self, data):
return(data)

@Decorator('key')
def function_2(self, data):
return(data)

@Decorator('key')
def function_3(self, data):
return(data)


@Decorator('key')
def test_f(data):
return(data)

# Test starts here
test_c = Test()
print(test_c.test('key', 'data'))
print(test_f('key', 'data'))
print(test_c.test('invalid', 'data'))
print(test_f('invalid', 'data'))
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Re: generator expression works in shell, NameError in script

[Mark Dickinson]

On Jun 19, 1:45 pm, Bruno Desthuilliers  wrote:
> [...]
> but it indeed looks like using bar.index *in a generator expression*
> fails (at least in 2.5.2) :
>
>   >>> class Foo(object):
> ...     bar = ['a', 'b', 'c']
> ...     baaz = list((bar.index(b), b) for b in bar)
> ...
> Traceback (most recent call last):
>    File "", line 1, in 
>    File "", line 3, in Foo
>    File "", line 3, in 
> NameError: global name 'bar' is not defined
>
> Looks like a bug to me :-/

I think it's working as intended:  name resolution for
nested scopes skips intermediate class scopes.  The
'Discussion' section of PEP 227 (Statically Nested Scopes)
is illuminating;  here's a snippet:

"""Names in class scope are not accessible.  Names are resolved in
the innermost enclosing function scope.  If a class definition
occurs in a chain of nested scopes, the resolution process skips
class definitions.  This rule prevents odd interactions between
class attributes and local variable access."""

Mark
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Re: persistent composites

[Aaron Brady]

On Jun 17, 3:53 pm, "Rhodri James" 
wrote:
> On Wed, 17 Jun 2009 16:06:22 +0100, Aaron Brady   
> wrote:
>
>
>
> > On Jun 16, 10:09 am, Mike Kazantsev  wrote:
> >> On Tue, 16 Jun 2009 06:57:13 -0700 (PDT)
>
> >> Aaron Brady  wrote:
> >> > Making the charitable interpretation that this was the extent of c-l-
> >> > py's support and enthusiasm for my idea, I will now go into mourning.
> >> > Death occurred at oh-eight-hundred.  Rest in peace, support &
> >> > enthusiasm.
>
> >> I've read this thread from the beginning, being tempted to insert
> >> remarks about shelve module or ORMs like SQLAlchemy, but that'd be
> >> meaningless without the problem description, which I haven't seen
> >> anywhere. Is it some trick idea like "let's walk on our heads"?
>
> > More like bronze them, or hang them on a tackboard.  You haven't
> > convinced me that it's not a problem, or that it's an easy one.
>
> Unfortunately it's up to you to demonstrate that it is a problem,
> whichever of the many possible 'it's you're talking about.  So far,
> the question "Why would I want to use this?  What's the use case?"
> has gone unanswered, and I'm sure I'm not the only baffled by it.

I can demonstrate it's a problem; many things are.

The subject line says it all.  SQL will persist (and share for IPC,
after a fashion) sets of statically typed tuples.  But we have need
for sets of dynamically typed tuples, in volatile storage at the very
least, or no one would like Python.

Whether we have need for them in persistent storage remains to be
seen.

POSH Python Object SHaring has been at least one student's graduate
thesis.  It couldn't hurt to pursue it if one has time, as with many
things.  It's pretty likely my estimates of end user usefulness of
'KeepDB', say, derive sturdily and steadily from our estimated
popularity of Python.  So much for my motives, though not for my
opportunities.

My implementation has followed two separate paths: one using SQL for a
back-end host; the other using hand-coded bytes on disk, complete with
large file support using views, and on-disk (or in-buffer) memory
management, which incidentally I spoke up about about a year ago.  It
was the topic of an honors lecture in the Data Structures course in my
undergrad.  For the record, I still can't beat a log-N balanced tree
for finding free nodes, but I am operating on the assumption that the
smallest sufficient region is the best to return from 'alloc'.

You are not being any help, Rhodri, in your question.  Its chief
virtue is fidelity of programming, that is, what you write is most
true to what you mean.  If you have an object on disk, and want the
third element of its 'coords' list attribute, it's a waste to do
anything other than find its disk address, then the disk address of
its 'coords' attribute, then the disk address of the third element of
that, such as say, loading or worse, processing, the entire structure;
even if, and in light of parallel considerations about economic market
transparency and efficiency, that is to say, economy, maybe /
especially/ if, you are having a lowly machine make do.  You don't
want to open every box in your basement to find your tennis racket;
you want to open one box, find the racket in the index, then open all
and only the boxes that 'nestedly' contain the racket.  (Yes, that's /
all/ and /only/, or 'if and only if'-- not to be confused with 'one
and only'.)

It's more economic.
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Re: Is this pylint error message valid or silly?

[Matthew Wilson]

On Fri 19 Jun 2009 02:55:52 AM EDT, Terry Reedy wrote:
>> if c == "today":
>> c = datetime.today()
>
> Now I guess that you actually intend c to be passed as a datetime 
> object. You only used the string as a type annotation, not as a real 
> default value. Something like 'record_date = None' is better.

Thanks for the feedback.  I think I should have used a more obvious
string in my original example and a more descriptive parameter name.

So, pretend that instead of 

c="today"

I wrote 

record_date="defaults to today's date".   

I know my way is unorthodox, but I think it is a little bit more obvious
to the reader than

record_date=None

The None is a signal to use a default value, but that is only apparent
after reading the code.

Thanks again for the comments.

Matt
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Re: Status of Python threading support (GIL removal)?

[Tyler Laing]

This is a very long-running issue, that has been discussed many times. Here
are the two sides to keeping the gil or removing it:

Remove the GIL:

   - True multi-threaded programming
   - Scalable performance across a multi-core machine
   - Unfortunately, this causes a slow-down in single core/thread
   performance
   - Most of the slow down comes from Python's Reference counting, as every
   function is supposed to increase and decrease the references... which leads
   to a lot of synchronization and checking of locks.
   - It makes the core interpreter much more complex

Keeping the GIL:

   - Processes should be used instead of threads. Look at Erlang, THE model
   of concurrency. It uses a process model for concurrency and message passing,
   rather than threads. This means you avoid deadlocks, livelocks, race
   conditions(not entirely, but they are reduced)
   - C extensions can still gain really impressive multi-threaded
   performance. My C extension, a wrapper around ffmpeg, releases the GIL for
   90% or so of its processing time, so all other threads are still extremely
   responsive.
   - It allows python to stay simple, understandable, and offer good
   performance, if you know how to use it properly.

Basically the two sides are that you it ends up slowing things down, it
makes the interpreter more complex vs you should use processes instead, and
be smart about how you use the GIL.

-Tyler
On Fri, Jun 19, 2009 at 2:52 AM, Jure Erznožnik wrote:

> See here for introduction:
>
> http://groups.google.si/group/comp.lang.python/browse_thread/thread/370f8a1747f0fb91
>
> Digging through my problem, I discovered Python isn't exactly thread
> safe and to solve the issue, there's this Global Interpreter Lock
> (GIL) in place.
> Effectively, this causes the interpreter to utilize one core when
> threading is not used and .95 of a core when threading is utilized.
>
> Is there any work in progess on core Python modules that will
> permanently resolve this issue?
> Is there any other way to work around the issue aside from forking new
> processes or using something else?
> --
> http://mail.python.org/mailman/listinfo/python-list
>



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Re: Status of Python threading support (GIL removal)?

[Ben Charrow]

Jure Erznožnik wrote:
> See here for introduction:
> http://groups.google.si/group/comp.lang.python/browse_thread/thread/370f8a1747f0fb91
> 
> Digging through my problem, I discovered Python isn't exactly thread
> safe and to solve the issue, there's this Global Interpreter Lock
> (GIL) in place.
> Effectively, this causes the interpreter to utilize one core when
> threading is not used and .95 of a core when threading is utilized.
> 
> Is there any work in progess on core Python modules that will
> permanently resolve this issue?
> Is there any other way to work around the issue aside from forking new
> processes or using something else?

There is a group of people working on an alternative implementation to Python
that, among other things, will not have a GIL:
http://code.google.com/p/unladen-swallow/

There was even a successful attempt to remove the GIL from CPython, but it
caused single threaded python code to be much slower.  See more here:
http://www.python.org/doc/faq/library/#can-t-we-get-rid-of-the-global-interpreter-lock

Cheers,
Ben

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Re: Is this pylint error message valid or silly?

[Rhodri James]

On Fri, 19 Jun 2009 14:36:01 +0100, Matthew Wilson  wrote:


On Fri 19 Jun 2009 02:55:52 AM EDT, Terry Reedy wrote:

if c == "today":
c = datetime.today()


Now I guess that you actually intend c to be passed as a datetime
object. You only used the string as a type annotation, not as a real
default value. Something like 'record_date = None' is better.


Thanks for the feedback.  I think I should have used a more obvious
string in my original example and a more descriptive parameter name.

So, pretend that instead of

c="today"

I wrote

record_date="defaults to today's date".

I know my way is unorthodox, but I think it is a little bit more obvious
to the reader than

record_date=None

The None is a signal to use a default value, but that is only apparent
after reading the code.


It's a very common idiom, however, and in addition

   record_data is None

is a cheap test, while

   record_data == "defaults to today's date"

is an expensive test as well as easy to mistype.

--
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Re: persistent composites

[Rhodri James]

On Fri, 19 Jun 2009 14:24:34 +0100, Aaron Brady   
wrote:



You are not being any help, Rhodri, in your question.


To you, perhaps not.  To me, it has at least had the effect of making
what you're trying to do (write a pythonic object database) clearer.

--
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Re: Status of Python threading support (GIL removal)?

[Martin von Loewis]

Digging through my problem, I discovered Python isn't exactly thread
safe and to solve the issue, there's this Global Interpreter Lock
(GIL) in place.


It's the opposite: Python is exactly thread safe precisely because it
has the GIL in place.


Is there any other way to work around the issue aside from forking new
processes or using something else?


If you know that your (C) code is thread safe on its own, you can 
release the GIL around long-running algorithms, thus using as many

CPUs as you have available, in a single process.

Regards,
Martin
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Re: Status of Python threading support (GIL removal)?

[Martin von Loewis]

Digging through my problem, I discovered Python isn't exactly thread
safe and to solve the issue, there's this Global Interpreter Lock
(GIL) in place.


It's the opposite: Python is exactly thread safe precisely because it
has the GIL in place.


Is there any other way to work around the issue aside from forking new
processes or using something else?


If you know that your (C) code is thread safe on its own, you can 
release the GIL around long-running algorithms, thus using as many

CPUs as you have available, in a single process.

Regards,
Martin
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Re: Is this pylint error message valid or silly?

[mblume]

Am Fri, 19 Jun 2009 00:56:18 + schrieb Matthew Wilson:

> Here's the code that I'm feeding to pylint:
> 
> $ cat f.py
> from datetime import datetime
> 
> def f(c="today"):
> 
> if c == "today":
> c = datetime.today()
> 
> return c.date()
> 
> 
> And here's what pylint says:
> 
> $ pylint -e f.py
> No config file found, using default configuration *
> Module f
> E: 10:f: Instance of 'str' has no 'date' member (but some types
> could not be inferred)
> 
> Is this a valid error message?  Is the code above bad?  If so, what is
> the right way?
> 
> I changed from using a string as the default to None, and then pylint
> didn't mind:
> 
> 
> $ cat f.py
> from datetime import datetime
> 
> def f(c=None):
> 
> if c is None:
> c = datetime.today()
> 
> return c.date()
> 
> $ pylint -e f.py
> No config file found, using default configuration
> 
> I don't see any difference between using a string vs None.  Both are
> immutable.  I find the string much more informative, since I can write
> out what I want.
> 
> Looking for comments.
> 
> Matt

Think of what happens if somebody calls
some_result = f("yesterday")

HTH
Martin
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multiprocessing and process run time

[Thomas Robitaille]

Hi,

I'm making use of the multiprocessing module, and I was wondering if there
is an easy way to find out how long a given process has been running for.
For example, if I do

import multiprocessing as mp
import time

def time_waster():
time.sleep(1000)

p = mp.Process(target=time_waster)

p.start()

Is there a way that I can then find how long p has been running for? I
figured I can use p.pid to get the PID of the process, but I'm not sure
where to go from there. Is there an easy way to do this?

Thanks,

Thomas
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Re: Status of Python threading support (GIL removal)?

[OdarR]

On 19 juin, 11:52, Jure Erznožnik  wrote:
> See here for 
> introduction:http://groups.google.si/group/comp.lang.python/browse_thread/thread/3...
>
> Digging through my problem, I discovered Python isn't exactly thread
> safe and to solve the issue, there's this Global Interpreter Lock
> (GIL) in place.
> Effectively, this causes the interpreter to utilize one core when
> threading is not used and .95 of a core when threading is utilized.
>
> Is there any work in progess on core Python modules that will
> permanently resolve this issue?
> Is there any other way to work around the issue aside from forking new
> processes or using something else?

hi,

please read this carefully,


there is a solution for Python on multi-core : multiprocessing api.
Really nice.

Keep real threads for common tasks like network stuff for example.

I recently complained too :-)



Olivier
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Re: Integer Division

[Grant Edwards]

On 2009-06-19, Anjanesh Lekshminarayanan  wrote:
 a = 1
 b = 25
 a / b
> 0
 float(a) / b
> 0.040001

>
 from __future__ import division
 a = 1
 b = 25
 a / b
> 0.040001

>
> In what simple way can I get just 0.04 ?

You can't.  There _is_no_ 0.04 when using binary IEEE floating
point (which is what's used for floats on any computer you're
likely to run across).

You could use some other data type (rationals, BCD floats,
etc.).

-- 
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  at   the divorce rate among
   visi.comunmarried Catholic Alaskan
   females!!
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Retrieving column values by column name with MySQLdb

[jorma kala]

Hi,
Is there a way of retrieving the value of columns in the rows returned by
fetchall, by column name instead of index on the row?
Code Snippet:

 query="select * from employees"
 db=MySQLdb.connect(host=host,user=user,passwd=passwd,db=database)
 cursor = db.cursor ()
 cursor.execute (query)
 rows = cursor.fetchall ()

  for row in rows:
   print row[0]


Instead of specifying the index of the row to retrieve the first column
(row[0]), I'd like to retrieve the value of the first column by column name.
Something like row.get('employee_id')
Is something of the sort possible with Mysqdb?
Thanks very much.
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Re: persistent composites

[Aahz]

In article ,
Aaron Brady   wrote:
>
>You are not being any help, Rhodri, in your question.  

Maybe not, but honestly, you're getting pretty close to going back in my
killfile.  Although you're no longer trolling this group, I find your
writing difficult to read at best; answering questions from people like
Rhodri is about your only chance to reach people like me.  Even without
the killfile, I'm skipping about 60-80% of your posts.  It's a free
Usenet, of course, so you're under no obligation to pay any attention to
me, but I think you ought to consider the merits of changing your
opinion of Rhodri's questions.

Side note: the rhetorical trick of inserting a person's name in a
statement is often intended and received as a mildly patronizing insult.
It's not at all clear to me whether that was your intent; if not, you
might want to change your writing style a bit.
-- 
Aahz (a...@pythoncraft.com)   <*> http://www.pythoncraft.com/

"as long as we like the same operating system, things are cool." --piranha
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Re: Calling subprocess with arguments

[Tyler Laing]

So no one has an answer for why passing flags and the values the flags need
through subprocess does not work? I would like an answer. I've examined all
the examples I could find online, which were all toy examples, and not
helpful to my problem.

On Thu, Jun 18, 2009 at 7:40 PM, Tyler Laing  wrote:

> I've been trying any variation I can think of to do this properly, but
> here's my problem:
>
> I want to execute this command string: vlc -I rc
>
> This allows vlc to be controlled via  a remote interface instead of the
> normal gui interface.
>
> Now, say, I try this from subprocess:
>
> >>>p=subprocess.Popen('vlc -I rc test.avi'.split(' '), shell=False,
> stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
>
> But I don't get the remote interface. I get the normal gui interface. So
> how do I do it? I've tried passing ['vlc', '-I', 'rc'], I've tried ['-I',
> 'rc'] with executable set to 'vlc'. I've had shell=True, I've had
> shell=False. I've tried all these combinations.
>
> What am I doing wrong?
>
> --
> Visit my blog at http://oddco.ca/zeroth/zblog
>



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Re: multiprocessing and process run time

[Mike Kazantsev]

On Fri, 19 Jun 2009 07:40:11 -0700 (PDT)
Thomas Robitaille  wrote:

> I'm making use of the multiprocessing module, and I was wondering if there
> is an easy way to find out how long a given process has been running for.
> For example, if I do
> 
> import multiprocessing as mp
> import time
> 
> def time_waster():
> time.sleep(1000)
> 
> p = mp.Process(target=time_waster)
> 
> p.start()
> 
> Is there a way that I can then find how long p has been running for? I
> figured I can use p.pid to get the PID of the process, but I'm not sure
> where to go from there. Is there an easy way to do this?

If you use unix-like platform (e.g. linux) you can just use 'ps -e -o
pid,start_time | grep '.
I'd used procpy to do ps-like stuff in python since it's a wrapper
around the same procps library, prehaps it can get the same results as
well, w/o having to invoke shell commands:

  http://code.google.com/p/procpy/

-- 
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Re: Calling subprocess with arguments

[Javier Collado]

Hello,

The problem might be that, aside from creating the Popen object, to
get the command run you need to call 'communicate' (other options, not
used with the Popen object directly, are 'call' or 'waitpid' as
explained in the documentation). Did you do that?

Best regards,
Javier

2009/6/19 Tyler Laing :
> So no one has an answer for why passing flags and the values the flags need
> through subprocess does not work? I would like an answer. I've examined all
> the examples I could find online, which were all toy examples, and not
> helpful to my problem.
>
> On Thu, Jun 18, 2009 at 7:40 PM, Tyler Laing  wrote:
>>
>> I've been trying any variation I can think of to do this properly, but
>> here's my problem:
>>
>> I want to execute this command string: vlc -I rc
>>
>> This allows vlc to be controlled via  a remote interface instead of the
>> normal gui interface.
>>
>> Now, say, I try this from subprocess:
>>
>> >>>p=subprocess.Popen('vlc -I rc test.avi'.split(' '), shell=False,
>> >>> stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
>>
>> But I don't get the remote interface. I get the normal gui interface. So
>> how do I do it? I've tried passing ['vlc', '-I', 'rc'], I've tried ['-I',
>> 'rc'] with executable set to 'vlc'. I've had shell=True, I've had
>> shell=False. I've tried all these combinations.
>>
>> What am I doing wrong?
>>
>> --
>> Visit my blog at http://oddco.ca/zeroth/zblog
>
>
>
> --
> Visit my blog at http://oddco.ca/zeroth/zblog
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>
>
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Re: GUI(eclipse+pydev/SPE) freeze when doing python auto-completion under Linux

[Fabio Zadrozny]

On Fri, Jun 19, 2009 at 12:22 AM, Wei, Xiaohai wrote:
> Thanks for your reply.
>
> where is the error log? I can not find it at /var/log

Take a look at http://pydev.sourceforge.net/faq.html#how_do_i_report_a_bug
(it gives the details on how to find the needed info).

> I have a virtual network card to bridge kvm virtual machine. will it cause
> problem?

Not sure... What I know is that pydev creates a shell and connects to
it through 127.0.0.1, so, if that fails, that could be a problem.

> as you said configuration of interpretor, how should I configure the
> interpretor?

Please follow the getting started tutorial for that:
http://fabioz.com/pydev/manual_101_root.html

Cheers,

Fabio

>
> Thanks
>
> James
>
> On Fri, Jun 19, 2009 at 9:32 AM, Fabio Zadrozny  wrote:
>>
>> > yes, the same problem even on an empty program. every file has the same
>> > problem.
>> >
>> > for example, if I new a file and input the following:
>> > import os
>> > os.
>> > after I input '.', it will pop up the window, and i can select the
>> > function
>> > of os module or continue input. but after that, no action can be taken
>> > for
>> > this file unless I switch to other files and then switch back.
>>
>> If it's in pydev, there's probably some problem in your interpreter
>> configuration (when you do os. it'll spawn a shell to gather the
>> completions -- but that should be pretty quick unless you have some
>> firewall that's preventing the communication or the spawn didn't go
>> well -- check your error log to see if you have any errors... In linux
>> I've seen some problems when connecting to 127.0.0.1 while having ipv6
>> enabled or in a network card misconfiguration that could cause
>> problems too).
>>
>> Cheers,
>>
>> Fabio
>>
>>
>> >
>> > On Thu, Jun 18, 2009 at 10:57 AM, Tyler Laing 
>> > wrote:
>> >>
>> >> Do you experience the same problem even on an empty program file or is
>> >> it
>> >> limited to just one file?
>> >>
>> >> -Tyler
>> >>
>> >> On Wed, Jun 17, 2009 at 7:47 PM, Wei, James  wrote:
>> >>>
>> >>> On Jun 18, 10:45 am, "Wei, James"  wrote:
>> >>> > When I am editing python program with SPE, I found that SPE will
>> >>> > freeze when it is doing auto-completion. The behavior is very
>> >>> > strange
>> >>> > that I can not edit the file again. If I switch to another file and
>> >>> > then switch back, I can edit it again.
>> >>> >
>> >>> > So I switch to eclipse+pydev, but I found the same thing happen. So
>> >>> > I
>> >>> > think it is not the problem of SPE or eclipse or pydev.
>> >>> >
>> >>> > If I disable auto-completion function in SPE or Eclipse+PyDev, it
>> >>> > will
>> >>> > not freeze any longer.
>> >>> >
>> >>> > Anybody can give me some hints?
>> >>> >
>> >>> > I am using Ubuntu 8.10 and updated to latest. All packages is
>> >>> > installed through package manager.
>> >>>
>> >>> the only thing I googled related with it is
>> >>>
>> >>>
>> >>>
>> >>> http://www.nabble.com/-pydev---Users--jython-2.5b1-Froze-eclipse-on-autocomplete-td21394274.html
>> >>>
>> >>> but I think they are different.
>> >>>
>> >>> --
>> >>> http://mail.python.org/mailman/listinfo/python-list
>> >>
>> >>
>> >>
>> >> --
>> >> Visit my blog at http://oddco.ca/zeroth/zblog
>> >
>> >
>> >
>> > --
>> > Best wishes to you.
>> >
>> > Yours sincerely
>> >
>> > Xiaohai Wei
>> > wist...@ustc.edu
>> >
>> > --
>> > http://mail.python.org/mailman/listinfo/python-list
>> >
>> >
>
>
>
> --
> Best wishes to you.
>
> Yours sincerely
>
> Xiaohai Wei
> wist...@ustc.edu
>
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Re: Calling subprocess with arguments

[Tyler Laing]

I can't use communicate, as it waits for the child process to terminate.
Basically it blocks. I'm trying to have dynamic communication between the
python program, and vlc.

On Fri, Jun 19, 2009 at 8:05 AM, Charles Yeomans wrote:

>
> On Jun 19, 2009, at 10:55 AM, Tyler Laing wrote:
>
> So no one has an answer for why passing flags and the values the flags need
> through subprocess does not work? I would like an answer. I've examined all
> the examples I could find online, which were all toy examples, and not
> helpful to my problem.
>
> On Thu, Jun 18, 2009 at 7:40 PM, Tyler Laing  wrote:
>
>> I've been trying any variation I can think of to do this properly, but
>> here's my problem:
>>
>> I want to execute this command string: vlc -I rc
>>
>> This allows vlc to be controlled via  a remote interface instead of the
>> normal gui interface.
>>
>> Now, say, I try this from subprocess:
>>
>> >>>p=subprocess.Popen('vlc -I rc test.avi'.split(' '), shell=False,
>> stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
>>
>> But I don't get the remote interface. I get the normal gui interface. So
>> how do I do it? I've tried passing ['vlc', '-I', 'rc'], I've tried ['-I',
>> 'rc'] with executable set to 'vlc'. I've had shell=True, I've had
>> shell=False. I've tried all these combinations.
>>
>> What am I doing wrong?
>>
>
> You might try
>
> p = subprocess.Popen('vlc -I rc test.avi', ...
>
> Charles Yeomans
>
>
>


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Re: Calling subprocess with arguments

[Mike Kazantsev]

On Fri, 19 Jun 2009 07:55:19 -0700
Tyler Laing  wrote:

> I want to execute this command string: vlc -I rc
>
> This allows vlc to be controlled via  a remote interface instead of the
> normal gui interface.
>
> Now, say, I try this from subprocess:
>
> >>>p=subprocess.Popen('vlc -I rc test.avi'.split(' '), shell=False,
> stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
>
> But I don't get the remote interface. I get the normal gui interface. So
> how do I do it? I've tried passing ['vlc', '-I', 'rc'], I've tried ['-I',
> 'rc'] with executable set to 'vlc'. I've had shell=True, I've had
> shell=False. I've tried all these combinations.
>
> What am I doing wrong?

Write a simple script:

  #!/usr/bin/env python
  import sys
  open('/tmp/argv', 'w').write(repr(sys.argv))

And replace 'vlc' with a path to this script, then invoke it from a
shell, compare the results.
If it gets the right stuff, try the same with os.environ (prehaps vlc
keeps socket location there, just like ssh/gpg-agents?).

-- 
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Re: Calling subprocess with arguments

[Mike Kazantsev]

On Fri, 19 Jun 2009 08:07:29 -0700
Tyler Laing  wrote:

> I can't use communicate, as it waits for the child process to terminate.
> Basically it blocks. I'm trying to have dynamic communication between the
> python program, and vlc.

Unfortunately, subprocess module doesn't allow it out-of-the-box, but
you can use fnctl calls to perform non-blocking reads/writes on it's
pipes, like this:

  flags = fcntl.fcntl(fd, fcntl.F_GETFL)
  fcntl.fcntl(fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)

After that, you can grab all the available data from the pipe at any
given time w/o blocking.

Try this recipe:

  http://code.activestate.com/recipes/576759/

-- 
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Re: multiprocessing and process run time

[OdarR]

On 19 juin, 16:40, Thomas Robitaille 
wrote:
> Hi,
>
> I'm making use of the multiprocessing module, and I was wondering if there
> is an easy way to find out how long a given process has been running for.
> For example, if I do
>
> import multiprocessing as mp
> import time
>
> def time_waster():
>     time.sleep(1000)
>
> p = mp.Process(target=time_waster)
>
> p.start()
>
> Is there a way that I can then find how long p has been running for? I
> figured I can use p.pid to get the PID of the process, but I'm not sure
> where to go from there. Is there an easy way to do this?

Something like :

import multiprocessing as mp
import time

q_out = mp.Queue()

def time_waster(qo):
time.sleep(5)
qo.put('stopped at ' + time.ctime(time.time()))

def main():
p = mp.Process(target=time_waster, args=(q_out,))
print "start at: " + time.ctime(time.time())
p.start()
p.join()
print q_out.get()

if __name__ == "__main__":
main()


The Queue (the one from multiprocessing ! don't mix with the Queue
module) is used as a safe exchange object between the parent and all
the child.

Olivier
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Re: Retrieving column values by column name with MySQLdb

[Kushal Kumaran]

On Fri, Jun 19, 2009 at 8:16 PM, jorma kala wrote:
> Hi,
> Is there a way of retrieving the value of columns in the rows returned by
> fetchall, by column name instead of index on the row?
> Code Snippet:
>
>  query="select * from employees"
>  db=MySQLdb.connect(host=host,user=user,passwd=passwd,db=database)
>  cursor = db.cursor ()
>  cursor.execute (query)
>  rows = cursor.fetchall ()
>
>   for row in rows:
>    print row[0]
>
>
> Instead of specifying the index of the row to retrieve the first column
> (row[0]), I'd like to retrieve the value of the first column by column name.
> Something like row.get('employee_id')
> Is something of the sort possible with Mysqdb?
> Thanks very much.
>

Use a DictCursor:

import MySQLdb.cursors

.
.
.
 cursor = db.cursor (MySQLdb.cursors.DictCursor)
 cursor.execute (query)
 rows = cursor.fetchall ()

  for row in rows:
   print row['employee_id']

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Re: fastest native python database?

[Ethan Furman]

Ethan Furman wrote:

This body part will be downloaded on demand.




Not sure what happened there... here's the text...

Howdy, Pierre!

I have also written a pure Python implementation of a database, one that 
uses dBase III or VFP 6 .dbf files.  Any chance you could throw it into 
the mix to see how quickly (or slowly!) it runs?


The code to run the same steps are (after an import dbf):

#insert test
table = dbf.Table('/tmp/tmptable', 'a N(6.0), b N(6.0), c C(100)')
# if recs is list of tuples
for rec in recs:
   table.append(rec)
# elif recs is list of lists
#for a, b, c in recs:
#   current = table.append()
#   current.a = a
#   current.b = b
#   current.c = c

#select1 test
for i in range(100):
   nb = len(table)
   if nb:
  avg = sum([record.b for record in table])/nb

#select2 test
for num_string in num_strings:
records = table.find({'c':'%s'%num_string}, contained=True)
nb = len(records)
if nb:
   avg = sum([record.b for record in records])/nb

#delete1 test
for record in table:
   if 'fifty' in record.c:
  record.delete_record()
# to purge the records would then require a table.pack()

#delete2 test
for rec in table:
   if 10 < rec.a < 2:
  rec.delete_record()
# again, permanent deletion requires a table.pack()

#update1 test
table.order('a')
for i in range(100):  # update description says 1000, update code is 100
   records = table.query(python='10*%d <= a < 10*%d' %(10*i,10*(i+1)))
   for rec in records:
  rec.b *= 2

#update2 test
records = table.query(python="0 <= a < 1000")
for rec in records:
   rec.c = new_c[rec.a]

Thanks, I hope!  :)

~Ethan~
http://groups.google.com/group/python-dbase
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Re: Calling subprocess with arguments

[Tyler Laing]

Thanks mike, the idea that maybe some of the info isn't being passed is
certainly interesting.

Here's the output of os.environ and sys.argv:

ty...@surak:~$ cat environ
{'XAUTHORITY': '/home/tyler/.Xauthority', 'GNOME_DESKTOP_SESSION_ID':
'this-is-deprecated', 'ORBIT_SOCKETDIR': '/tmp/orbit-tyler', 'LESSOPEN': '|
/usr/bin/lesspipe %s', 'LOGNAME': 'tyler', 'USER': 'tyler', 'PATH':
'/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games',
'HOME': '/home/tyler', 'WINDOWPATH': '7', 'SSH_AGENT_PID': '3235', 'LANG':
'en_CA.UTF-8', 'TERM': 'xterm', 'SHELL': '/bin/bash', 'XDG_SESSION_COOKIE':
'c40b96e13a53e01daf91b3c24a37cc3f-1245418411.623618-1455422513',
'SESSION_MANAGER': 'local/Surak:/tmp/.ICE-unix/3078', 'SHLVL': '1',
'DISPLAY': ':0.0', 'WINDOWID': '62914615', 'COLUMNS': '80',
'GPG_AGENT_INFO': '/tmp/seahorse-WkObD8/S.gpg-agent:3260:1', 'USERNAME':
'tyler', 'GDM_XSERVER_LOCATION': 'local', 'GTK_RC_FILES':
'/etc/gtk/gtkrc:/home/tyler/.gtkrc-1.2-gnome2', 'LINES': '24',
'SSH_AUTH_SOCK': '/tmp/keyring-glzV2L/socket.ssh', 'DESKTOP_SESSION':
'default', 'GDMSESSION': 'default', 'DBUS_SESSION_BUS_ADDRESS':
'unix:abstract=/tmp/dbus-HXzG5Pt75p,guid=9fc00f8a914d6f800340ca634a3b93ac',
'_': '/usr/bin/python', 'GTK_MODULES': 'canberra-gtk-module',
'GNOME_KEYRING_SOCKET': '/tmp/keyring-glzV2L/socket', 'LESSCLOSE':
'/usr/bin/lesspipe %s %s', 'GNOME_KEYRING_PID': '3065', '__GL_YIELD':
'NOTHING', 'GDM_LANG': 'en_CA.UTF-8', 'HISTCONTROL': 'ignoreboth',
'XDG_DATA_DIRS': '/usr/local/share/:/usr/share/:/usr/share/gdm/', 'PWD':
'/home/tyler', 'COLORTERM': 'gnome-terminal', 'FROM_WRAPPER': 'yes',
'LS_COLORS':
'no=00:fi=00:di=01;34:ln=01;36:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:su=37;41:sg=30;43:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.svgz=01;31:*.arj=01;31:*.taz=01;31:*.lzh=01;31:*.lzma=01;31:*.zip=01;31:*.z=01;31:*.Z=01;31:*.dz=01;31:*.gz=01;31:*.bz2=01;31:*.bz=01;31:*.tbz2=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.rar=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.jpg=01;35:*.jpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.aac=00;36:*.au=00;36:*.flac=00;36:*.mid=00;36:*.midi=00;36:*.mka=00;36:*.mp3=00;36:*.mpc=00;36:*.ogg=00;36:*.ra=00;36:*.wav=00;36:'}
ty...@surak:~$ cat argv
['./testsub.py', '-I', 'rc']

On Fri, Jun 19, 2009 at 8:21 AM, Mike Kazantsev wrote:

> On Fri, 19 Jun 2009 08:07:29 -0700
> Tyler Laing  wrote:
>
> > I can't use communicate, as it waits for the child process to terminate.
> > Basically it blocks. I'm trying to have dynamic communication between the
> > python program, and vlc.
>
> Unfortunately, subprocess module doesn't allow it out-of-the-box, but
> you can use fnctl calls to perform non-blocking reads/writes on it's
> pipes, like this:
>
>  flags = fcntl.fcntl(fd, fcntl.F_GETFL)
>  fcntl.fcntl(fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)
>
> After that, you can grab all the available data from the pipe at any
> given time w/o blocking.
>
> Try this recipe:
>
>  http://code.activestate.com/recipes/576759/
>
> --
> Mike Kazantsev // fraggod.net
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>
>


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Re: Retrieving column values by column name with MySQLdb

[Tim Chase]

jorma kala wrote:

Hi,
Is there a way of retrieving the value of columns in the rows returned by
fetchall, by column name instead of index on the row?
Code Snippet:

 query="select * from employees"
 db=MySQLdb.connect(host=host,user=user,passwd=passwd,db=database)
 cursor = db.cursor ()
 cursor.execute (query)
 rows = cursor.fetchall ()

  for row in rows:
   print row[0]


Instead of specifying the index of the row to retrieve the first column
(row[0]), I'd like to retrieve the value of the first column by column name.
Something like row.get('employee_id')
Is something of the sort possible with Mysqdb?



Mike gave you a good answer, though I think it's MySQL specific. 
For a more generic solution:


  cursor.execute(query)
  name_to_index = dict(
(d[0], i)
for i, d
in enumerate(cursor.description)
)
  rows = cursor.fetchall()
  for row in rows:
print row[name_to_index['employee_id']]

Or in case you have lots of column-names, a simple lambda can 
ease the typing required:


  for row in rows:
item = lambda col_name: row[name_to_index[col_name]]
print item('employee_id')

The built-in sqlite3 module also has a way to tell results to 
come back as a dict[1]


Note in each case the column-name indexing is case-sensitive.


Hope this helps,

-tim

[1]
http://docs.python.org/library/sqlite3.html#sqlite3.Connection.row_factory






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Re: sqlite3, OperationalError: no such column, shouldn't that ne a ProgrammingError?

[John Machin]

On Jun 19, 8:20 pm, Gerhard Häring  wrote:
> Gabriel Rossetti wrote:
> > Hello everyone,
>
> > I get an OperationalError with sqlite3 if I put the wrong column name,
> > but shouldn't that be a ProgrammingError instead? I read PEP 249 and it
> > says :
>
> > "        OperationalError
> >                    Exception raised for errors that are related to the
> >            database's operation and not necessarily under the control
> >            of the programmer, e.g. an unexpected disconnect occurs,
> >            the data source name is not found, a transaction could not
> >            be processed, a memory allocation error occurred during
> >            processing, etc.  It must be a subclass of DatabaseError.
> >                  ProgrammingError
> >                    Exception raised for programming errors, e.g. table not
> >            found or already exists, syntax error in the SQL
> >            statement, wrong number of parameters specified, etc.  It
> >            must be a subclass of DatabaseError.
> > "
>
> > and to me it sounds more like a programming error than an operational
> > error.
>
> I agree. But I can't help you there.
>
> See _pysqlite_seterror() 
> athttp://oss.itsystementwicklung.de/trac/pysqlite/browser/src/util.c
>
> What I do is map SQLite error codes to DB-API exceptions. And SQLite
> reports your error as generic SQLITE_ERROR, which is mapped to
> OperationalError.

Hi Gerhard,

In http://www.sqlite.org/c3ref/prepare.html it says """When an error
occurs, sqlite3_step() will return one of the detailed error codes or
extended error codes. The legacy behavior was that sqlite3_step()
would only return a generic SQLITE_ERROR result code and you would
have to make a second call to sqlite3_reset() in order to find the
underlying cause of the problem. With the "v2" prepare interfaces, the
underlying reason for the error is returned immediately."""

Are you using sqlite3_prepare() or sqlite3_prepare_v2()?
sqlite3_errcode() or sqlite3_extended_errcode()?

Cheers,
John
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Re: Decorator question (how to test if decorated function is in a class)

[Bruno Desthuilliers]

Martin P. Hellwig a écrit :

Hi all,

I have been trying out to wrap my mind around the advantages of 
decorators and thought I found a use in one of my experiments. (see code 
after my sig).


Although it works, I think it should be able to do it better.
My particular problem is that I want to remove an argument (say always 
the first one) when the decorated function is called.


However if the function is defined in a class the first argument is self 
and thus the second argument should be removed.


You'll have the same problem with a function defined outside a class 
then "attached" to the class, ie:


def func(...):
   pass


class Foo(object):
   pass

Foo.meth = func


Since I like to have a more general DRY approach I want to test if the 
decorated function is defined in a class or not thus knowing that the 
first argument is self and must be preserved.


Short answer: this makes no sense.

I tried different approaches but all didn't work and looked very 
unpythonic (looking at the attributes, descriptors namespaces, id() of 
the function, the first argument and the decorator itself).


So is there a way to find out if the first argument is 'self' without 
making a false positive if the first argument is a class instance passed 
to a function?


The solution to your problem is elsewhere... Read the doc about the 
descriptor protocol, and how it's implemented by the function type to 
"turn" functions into methods when they are looked up as attribute of a 
class...



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Re: Retrieving column values by column name with MySQLdb

[Mike Kazantsev]

On Fri, 19 Jun 2009 15:46:46 +0100
jorma kala  wrote:

> Is there a way of retrieving the value of columns in the rows returned by
> fetchall, by column name instead of index on the row?

Try this:

  db = MySQLdb.Connection(host=host,user=user,passwd=passwd,db=database)
  db.query(query)
  result = db.store_result()
  data = result.fetch_row(maxrows=0, how=1)

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Re: Retrieving column values by column name with MySQLdb

[Mike Kazantsev]

On Fri, 19 Jun 2009 10:32:32 -0500
Tim Chase  wrote:

> Mike gave you a good answer, though I think it's MySQL specific. 

I don't have to deal with MySQL frequently but I've remembered that I
used got the fields out somehow, and now, looking at the code, I wonder
myself, why "how" is 1 and wtf is this "how", anyway!? ;)

I can't seem to find any mention of such methods in documentation and
even python source, guess they are implemented directly in underlying
C lib.
Hope I learned to abstract from such syntax since then, I sure do...

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Re: Is this pylint error message valid or silly?

[Terry Reedy]

Matthew Wilson wrote:


Thanks for the feedback.  I think I should have used a more obvious
string in my original example and a more descriptive parameter name.

So, pretend that instead of 


c="today"

I wrote 

record_date="defaults to today's date".   


I know my way is unorthodox,


Which is fine. Just do not by surprised when a fake default fakes out 
pylint, which by its nature, must embody the orthodoxy of its author ;-)
To win general acceptance, that in turn must match the orthodoxy of the 
general audience.



 but I think it is a little bit more obvious

to the reader than

record_date=None

The None is a signal to use a default value, but that is only apparent
after reading the code.

Thanks again for the comments.

Matt


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Re: Status of Python threading support (GIL removal)?

[Stefan Behnel]

Jure Erznožnik wrote:
> See here for introduction:
> http://groups.google.si/group/comp.lang.python/browse_thread/thread/370f8a1747f0fb91
> 
> Digging through my problem, I discovered Python isn't exactly thread
> safe and to solve the issue, there's this Global Interpreter Lock
> (GIL) in place.
> Effectively, this causes the interpreter to utilize one core when
> threading is not used and .95 of a core when threading is utilized.

You might want to read about "The Problem with Threads":

http://www.eecs.berkeley.edu/Pubs/TechRpts/2006/EECS-2006-1.pdf

and then decide to switch to an appropriate concurrency model for your use
case.

Stefan
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Re: Calling subprocess with arguments

[Mike Kazantsev]

On Fri, 19 Jun 2009 08:28:17 -0700
Tyler Laing  wrote:

> Thanks mike, the idea that maybe some of the info isn't being passed is
> certainly interesting.
> 
> Here's the output of os.environ and sys.argv:
>
...

I'm afraid these doesn't make much sense without the output from the
second results, from py itself. My suggestion was just to compare them
- pop the py shell, eval the outputs into two sets, do the diff and
you'll see it at once.
If there's an empty set then I guess it's pretty safe to assume that
python creates subprocess in the same way the shell does.

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Re: Integer Division

[Terry Reedy]

Anjanesh Lekshminarayanan wrote:

a = 1
b = 25
a / b

0

float(a) / b

0.040001


from __future__ import division
a = 1
b = 25
a / b

0.040001

In what simple way can I get just 0.04 ?


Short answer: use 3.1:
>>> 1//25
0
>>> 1/25
0.04
;-)

But you should really try to understand the answers others gave.

tjr

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Re: Calling subprocess with arguments

[Mike Kazantsev]

On Fri, 19 Jun 2009 22:00:28 +0600
Mike Kazantsev  wrote:

> On Fri, 19 Jun 2009 08:28:17 -0700
> Tyler Laing  wrote:
> 
> > Thanks mike, the idea that maybe some of the info isn't being passed is
> > certainly interesting.
> > 
> > Here's the output of os.environ and sys.argv:
> >
> ...
> 
> I'm afraid these doesn't make much sense without the output from the
> second results, from py itself. My suggestion was just to compare them
> - pop the py shell, eval the outputs into two sets, do the diff and
> you'll see it at once.
> If there's an empty set then I guess it's pretty safe to assume that
> python creates subprocess in the same way the shell does.

Just thought of one more really simple thing I've missed: vlc might
expect it's remote to work with tty, so when py shoves it a pipe
instead, it automatically switches to non-interactive mode.

You can remedy that a bit by superclassing subprocess.Popen, replacing
pipes with pty, but they are quite hard to work with, prehaps pexpect
module would be of some use there:

  http://pypi.python.org/pypi/pexpect/

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Re: Status of Python threading support (GIL removal)?

[Terry Reedy]

Jure Erznožnik wrote:

See here for introduction:
http://groups.google.si/group/comp.lang.python/browse_thread/thread/370f8a1747f0fb91

Digging through my problem, I discovered Python isn't exactly thread
safe and to solve the issue, there's this Global Interpreter Lock
(GIL) in place.
Effectively, this causes the interpreter to utilize one core when
threading is not used and .95 of a core when threading is utilized.


Python does not have (or not have) GIL.
It is an implementation issue.
CPython uses it, to good effect.


Is there any work in progess on core Python modules that will
permanently resolve this issue?
Is there any other way to work around the issue aside from forking new
processes or using something else?


Use one of the other implementations.
Jython, IronPython, Pypy, ???

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n00b confusion re: local variable referenced before assignment error

[Wells Oliver]

Writing a class which essentially spiders a site and saves the files
locally. On a URLError exception, it sleeps for a second and tries again (on
404 it just moves on). The relevant bit of code, including the offending
method:

class Handler(threading.Thread):
def __init__(self, url):
threading.Thread.__init__(self)
self.url = url

def save(self, uri, location):
try:
handler = urllib2.urlopen(uri)
except urllib2.HTTPError, e:
if e.code == 404:
return
else:
print "retrying %s (HTTPError)" % uri
time.sleep(1)
self.save(uri, location)
except urllib2.URLError, e:
print "retrying %s" % uri
time.sleep(1)
self.save(uri, location)

if not os.path.exists(os.path.dirname(location)):
os.makedirs(os.path.dirname(location))

file = open(location, "w")
file.write(handler.read())
file.close()

...

But what I am seeing is that after a retry (on catching a URLError
exception), I see bunches of "UnboundLocalError: local variable 'handler'
referenced before assignment" errors on line 38, which is the
"file.write(handler.read())" line..

What gives?

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Re: Calling subprocess with arguments

[Tyler Laing]

Sorry, XD. I'll ask the VLC people if they happen to know why VLC won't open
up the remote interface.

-Tyler

On Fri, Jun 19, 2009 at 9:09 AM, Mike Kazantsev wrote:

> On Fri, 19 Jun 2009 22:00:28 +0600
> Mike Kazantsev  wrote:
>
> > On Fri, 19 Jun 2009 08:28:17 -0700
> > Tyler Laing  wrote:
> >
> > > Thanks mike, the idea that maybe some of the info isn't being passed is
> > > certainly interesting.
> > >
> > > Here's the output of os.environ and sys.argv:
> > >
> > ...
> >
> > I'm afraid these doesn't make much sense without the output from the
> > second results, from py itself. My suggestion was just to compare them
> > - pop the py shell, eval the outputs into two sets, do the diff and
> > you'll see it at once.
> > If there's an empty set then I guess it's pretty safe to assume that
> > python creates subprocess in the same way the shell does.
>
> Just thought of one more really simple thing I've missed: vlc might
> expect it's remote to work with tty, so when py shoves it a pipe
> instead, it automatically switches to non-interactive mode.
>
> You can remedy that a bit by superclassing subprocess.Popen, replacing
> pipes with pty, but they are quite hard to work with, prehaps pexpect
> module would be of some use there:
>
>  http://pypi.python.org/pypi/pexpect/
>
> --
> Mike Kazantsev // fraggod.net
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>
>


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Re: n00b confusion re: local variable referenced before assignment error

[Mike Kazantsev]

On Fri, 19 Jun 2009 11:16:38 -0500
Wells Oliver  wrote:

> def save(self, uri, location):
> try:
> handler = urllib2.urlopen(uri)
> except urllib2.HTTPError, e:
> if e.code == 404:
> return
> else:
> print "retrying %s (HTTPError)" % uri
> time.sleep(1)
> self.save(uri, location)
> except urllib2.URLError, e:
> print "retrying %s" % uri
> time.sleep(1)
> self.save(uri, location)
> 
> if not os.path.exists(os.path.dirname(location)):
> os.makedirs(os.path.dirname(location))
> 
> file = open(location, "w")
> file.write(handler.read())
> file.close()


> But what I am seeing is that after a retry (on catching a URLError
> exception), I see bunches of "UnboundLocalError: local variable 'handler'
> referenced before assignment" errors on line 38, which is the
> "file.write(handler.read())" line..
> 
> What gives?

Why not?
Try fails, except calls retry and after the retry code execution
continues to the undefined "handler", since the try has failed here.
You might want to insert return or avoid (possibly endless) recursion
altogether - just wrap it into while loop with some counter (aka
max_tries).

Also, you can get rid of code duplication by catching some basic
urllib2 exception, then checking if it's urllib2.HTTPError and it's code
is 404, retrying ("continue" for the loop case) otherwise.

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Re: n00b confusion re: local variable referenced before assignment error

[Falcolas]

On Jun 19, 10:16 am, Wells Oliver  wrote:
> Writing a class which essentially spiders a site and saves the files
> locally. On a URLError exception, it sleeps for a second and tries again (on
> 404 it just moves on). The relevant bit of code, including the offending
> method:
>
> [snip]
>
> But what I am seeing is that after a retry (on catching a URLError
> exception), I see bunches of "UnboundLocalError: local variable 'handler'
> referenced before assignment" errors on line 38, which is the
> "file.write(handler.read())" line..
>
> What gives?

'Handler' is only assigned in the try statement, so if you error into
your exception clause, nothing will have been bound to the name
'handler', causing the exception you're seeing.
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Re: n00b confusion re: local variable referenced before assignment error

[Diez B. Roggisch]

Wells Oliver schrieb:
Writing a class which essentially spiders a site and saves the files 
locally. On a URLError exception, it sleeps for a second and tries again 
(on 404 it just moves on). The relevant bit of code, including the 
offending method:


class Handler(threading.Thread):
def __init__(self, url):
threading.Thread.__init__(self)
self.url = url

def save(self, uri, location):
try:
handler = urllib2.urlopen(uri)
except urllib2.HTTPError, e:
if e.code == 404:
return
else:
print "retrying %s (HTTPError)" % uri
time.sleep(1)
self.save(uri, location)
except urllib2.URLError, e:
print "retrying %s" % uri
time.sleep(1)
self.save(uri, location)

if not os.path.exists(os.path.dirname(location)):
os.makedirs(os.path.dirname(location))

file = open(location, "w")
file.write(handler.read())
file.close()

...

But what I am seeing is that after a retry (on catching a URLError 
exception), I see bunches of "UnboundLocalError: local variable 
'handler' referenced before assignment" errors on line 38, which is the 
"file.write(handler.read())" line..


Your code defines the name handler only if the urllib2.urlopen is 
successful. But you try later to access it uncoditionally, and of course 
that fails.


You need to put the file-stuff after the urlopen, inside the try-except.

Also note that python has no tail-recursion-optimization, so your method 
will recurse and at some point exhaust the stack if there are many errors.


You should consider writing it rather as while-loop, with breaking out 
of it when the page could be fetched.


Diez
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Re: Calling subprocess with arguments

[Tyler Laing]

It appears to be an issue specifically with VLC, not subprocess. Thank you
guys. The remote interface works through sockets, which is perfectly fine...
if I create a local socket, I can have it connect to the socket with command
line arguments.

On Fri, Jun 19, 2009 at 9:30 AM, Tyler Laing  wrote:

> Sorry, XD. I'll ask the VLC people if they happen to know why VLC won't
> open up the remote interface.
>
> -Tyler
>
> On Fri, Jun 19, 2009 at 9:09 AM, Mike Kazantsev wrote:
>
>> On Fri, 19 Jun 2009 22:00:28 +0600
>> Mike Kazantsev  wrote:
>>
>> > On Fri, 19 Jun 2009 08:28:17 -0700
>> > Tyler Laing  wrote:
>> >
>> > > Thanks mike, the idea that maybe some of the info isn't being passed
>> is
>> > > certainly interesting.
>> > >
>> > > Here's the output of os.environ and sys.argv:
>> > >
>> > ...
>> >
>> > I'm afraid these doesn't make much sense without the output from the
>> > second results, from py itself. My suggestion was just to compare them
>> > - pop the py shell, eval the outputs into two sets, do the diff and
>> > you'll see it at once.
>> > If there's an empty set then I guess it's pretty safe to assume that
>> > python creates subprocess in the same way the shell does.
>>
>> Just thought of one more really simple thing I've missed: vlc might
>> expect it's remote to work with tty, so when py shoves it a pipe
>> instead, it automatically switches to non-interactive mode.
>>
>> You can remedy that a bit by superclassing subprocess.Popen, replacing
>> pipes with pty, but they are quite hard to work with, prehaps pexpect
>> module would be of some use there:
>>
>>  http://pypi.python.org/pypi/pexpect/
>>
>> --
>> Mike Kazantsev // fraggod.net
>>
>> --
>> http://mail.python.org/mailman/listinfo/python-list
>>
>>
>
>
> --
> Visit my blog at http://oddco.ca/zeroth/zblog
>



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Re: Status of Python threading support (GIL removal)?

[OdarR]

On 19 juin, 16:16, Martin von Loewis  If you know that your (C) code is thread safe on its own, you can
> release the GIL around long-running algorithms, thus using as many
> CPUs as you have available, in a single process.

what do you mean ?

Cpython can't benefit from multi-core without multiple processes.

Olivier
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Re: Status of Python threading support (GIL removal)?

[Tyler Laing]

CPython itself can't... but the c extension can. Mine did.

On Fri, Jun 19, 2009 at 9:50 AM, OdarR  wrote:

> On 19 juin, 16:16, Martin von Loewis  > If you know that your (C) code is thread safe on its own, you can
> > release the GIL around long-running algorithms, thus using as many
> > CPUs as you have available, in a single process.
>
> what do you mean ?
>
> Cpython can't benefit from multi-core without multiple processes.
>
> Olivier
> --
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>



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Re: Status of Python threading support (GIL removal)?

[skip]

>> If you know that your (C) code is thread safe on its own, you can
>> release the GIL around long-running algorithms, thus using as many
>> CPUs as you have available, in a single process.

Olivier> what do you mean ?

Olivier> Cpython can't benefit from multi-core without multiple
Olivier> processes.

It can, precisely as Martin indicated.  Only one thread at a time can hold
the GIL.  That doesn't mean that multiple threads can't execute.  Suppose
you have two threads, one of which winds up executing some bit of C code
which doesn't mess with the Python run-time at all (say, a matrix multiply).
Before launching into the matrix multiply, the extension module releases the
GIL then performs the multiply.  With the GIL released another thread can
acquire it.  Once the multiply finishes the first thread needs to reacquire
the GIL before executing any calls into the Python runtime or returning.

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Re: Status of Python threading support (GIL removal)?

[OdarR]

On 19 juin, 19:13, s...@pobox.com wrote:
>     Olivier> what do you mean ?
>
>     Olivier> Cpython can't benefit from multi-core without multiple
>     Olivier> processes.
>
> It can, precisely as Martin indicated.  Only one thread at a time can hold
> the GIL.  That doesn't mean that multiple threads can't execute.  Suppose

I don't say multiple threads can't execute(?).
I say that with the Python library, I don't see (yet) benefit with
multiple threads *on* multiple CPU/core.

Ever seen this recent video/presentation ? :
http://blip.tv/file/2232410
http://www.dabeaz.com/python/GIL.pdf

> you have two threads, one of which winds up executing some bit of C code
> which doesn't mess with the Python run-time at all (say, a matrix multiply).

I don't know how to do that with common Python operations...
Only one thread will be really running at a time in memory (meanwhile
other thread are waiting).
Are you refering to a specialized code ?

> Before launching into the matrix multiply, the extension module releases the
> GIL then performs the multiply.  With the GIL released another thread can
> acquire it.  Once the multiply finishes the first thread needs to reacquire
> the GIL before executing any calls into the Python runtime or returning.

I don't see such improvement in the Python library, or maybe you can
indicate us some meaningfull example...?

I currently only use CPython, with PIL, Reportlab...etc.
I don't see improvement on a Core2duo CPU and Python. How to proceed
(following what you wrote) ?

A contrario, I saw *real* improvement on parallel computing with the
Py 2.6 multiprocessing module.

Olivier
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Convert hash to struct

[Amita Ekbote]

 Hello,

I am retrieving values from a database in the form of a dictionary so
I can access the values as d['column'] and I was wondering if there is
a way to convert the hash to a struct like format so i can just say
d.column. Makes it easier to read and understand.

Thanks
Amita

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Re: Measuring Fractal Dimension ?

[David C . Ullrich]

Evidently my posts are appearing, since I see replies.
I guess the question of why I don't see the posts themselves
\is ot here...

On Thu, 18 Jun 2009 17:01:12 -0700 (PDT), Mark Dickinson
 wrote:

>On Jun 18, 7:26 pm, David C. Ullrich  wrote:
>> On Wed, 17 Jun 2009 08:18:52 -0700 (PDT), Mark Dickinson
>> >Right.  Or rather, you treat it as the image of such a function,
>> >if you're being careful to distinguish the curve (a subset
>> >of R^2) from its parametrization (a continuous function
>> >R -> R**2).  It's the parametrization that's uniformly
>> >continuous, not the curve,
>>
>> Again, it doesn't really matter, but since you use the phrase
>> "if you're being careful": In fact what you say is exactly
>> backwards - if you're being careful that subset of the plane
>> is _not_ a curve (it's sometimes called the "trace" of the curve".
>
>Darn.  So I've been getting it wrong all this time.  Oh well,
>at least I'm not alone:
>
>"De?nition 1. A simple closed curve J, also called a
>Jordan curve, is the image of a continuous one-to-one
>function from R/Z to R2. [...]"
>
>- Tom Hales, in 'Jordan's Proof of the Jordan Curve Theorem'.
>
>"We say that Gamma is a curve if it is the image in
>the plane or in space of an interval [a, b] of real
>numbers of a continuous function gamma."
>
>- Claude Tricot, 'Curves and Fractal Dimension' (Springer, 1995).
>
>Perhaps your definition of curve isn't as universal or
>'official' as you seem to think it is?

Perhaps not. I'm very surprised to see those definitions; I've
been a mathematician for 25 years and I've never seen a
curve defined a subset of the plane.

Hmm. You left out a bit in the first definition you cite:

"A simple closed curve J, also called a Jordan curve, is the image
of a continuous one-to-one function from R/Z to R2. We assume that
each curve
comes with a fixed parametrization phi_J : R/Z ->¨ J. We call t in R/Z
the time
parameter. By abuse of notation, we write J(t) in R2 instead of phi_j
(t), using the
same notation for the function phi_J and its image J."

Close to sounding like he can't decide whether J is a set or a
function... Then later in the same paper

"Definition 2. A polygon is a Jordan curve that is a subset of a
finite union of
lines. A polygonal path is a continuous function P : [0, 1] ->¨ R2
that is a subset of
a finite union of lines. It is a polygonal arc, if it is 1 . 1."

By that definition a polygonal path is not a curve.

Worse: A polygonal path is a function from [0,1] to R^2
_that is a subset of a finite union of lines_. There's no
such thing - the _image_ of such a function can be a
subset of a finite union of lines.

Not that it matters, but his defintion of "polygonal path"
is, _if_ we're being very careful, self-contradictory.
So I don't think we can count that paper as a suitable
reference for what the _standard_ definitions are;
the standard definitions are not self-contradictory this way.

Then the second definition you cite: Amazon says the
prerequisites are two years of calculus. The stanard
meaning of log is log base e, even though it means
log base 10 in calculus.

>Mark

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Re: Convert hash to struct

[D'Arcy J.M. Cain]

On Fri, 19 Jun 2009 13:17:24 -0500
Amita Ekbote  wrote:
> I am retrieving values from a database in the form of a dictionary so
> I can access the values as d['column'] and I was wondering if there is
> a way to convert the hash to a struct like format so i can just say
> d.column. Makes it easier to read and understand.

Are there enough clues here?

class MyDict(dict):
def __getattribute__(self, name):
return dict.__getattribute__(self, name)

def __getattr__(self, name):
return self.get(name, 42)

x = MyDict({'a': 1, 'b': 2, 'values': 3})

print x.a
print x.z
print x.values

Big question - what should the last line display?  If you expect "3"
and not "" then
you need to reconsider the above implementation.  Thinking about the
question may change your opinion about this being a good idea after all.

-- 
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http://www.druid.net/darcy/|  and a sheep voting on
+1 416 425 1212 (DoD#0082)(eNTP)   |  what's for dinner.
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Re: walking a directory with very many files

[Lie Ryan]

Lawrence D'Oliveiro wrote:
> In message <%zv_l.19493$y61.5...@news-server.bigpond.net.au>, Lie Ryan 
> wrote:
> 
>> Yeah, it might be possible to just mv the file from outside, but not
>> being able to enter a directory just because you've got too many files
>> in it is kind of silly.
> 
> Sounds like a problem with your file/directory-manipulation tools.
> 

try an `ls` on a folder with 1+ files.

See how long is needed to print all the files.

Ok, now pipe ls to less, take three days to browse through all the
filenames to locate the file you want to see.

The file manipulation tool may not have problems with it; it's the user
that would have a hard time sorting through the huge amount of files.

Even with glob and grep, some types of queries are just too difficult or
is plain silly to write a full fledged one-time use program just to
locate a few files.
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Re: Convert hash to struct

[Lie Ryan]

Amita Ekbote wrote:
>  Hello,
> 
> I am retrieving values from a database in the form of a dictionary so
> I can access the values as d['column'] and I was wondering if there is
> a way to convert the hash to a struct like format so i can just say
> d.column. Makes it easier to read and understand.
> 
> Thanks
> Amita
> 

You may be able to update the class' dict:

>>> class MyDB(object):
... def __init__(self, di):
... self.__dict__.update(di)
...
>>> di = {'a':10, 'b': 20}
>>> d = MyDB(di)
>>> d
<__main__.MyDB object at 0x7f756b0d0b90>
>>> d.a
10
>>> d.b
20

but this might be a security risk, if you cannot trust the database or
its content.

It is much preferrable to use something like:

>>> class MyDB(object):
... def __init__(self, di):
... self.a = di['a']
... self.b = di['b']


since you now have full control of what collumns can go in and whatnot.
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Rich comparison methods don't work in sets?

[Gustavo Narea]

Hello, everyone.

I've noticed that if I have a class with so-called "rich comparison"
methods
(__eq__, __ne__, etc.), when its instances are included in a set,
set.__contains__/__eq__ won't call the .__eq__ method of the elements
and thus
the code below:
"""
obj1 = RichComparisonClass()
obj2 = RichComparisonClass()

set1 = set([obj1])
set2 = set([obj2])

if obj1 == obj2:
print "Objects 1 and 2 are equivalent"
else:
print "Objects 1 and 2 aren't equivalent"

if set1 == set2:
print "Sets 1 and 2 are equivalent"
else:
print "Sets 1 and 2 aren't equivalent"
"""

Would output:
"""
Objects 1 and 2 are equivalent
Sets 1 and 2 aren't equivalent
"""

instead of:
"""
Objects 1 and 2 are equivalent
Sets 1 and 2 are equivalent
"""

How can I work around this? The only solution that comes to my mind is
to
write a function like this:
"""
def same_sets(set1, set2):
if len(set1) != len(set2): return False
for element1 in set1:
found = False
for element2 in set2:
if element1 == element2:
found = True
break;
if not found:
return False
return True
"""

But I see it pretty ugly; also I'd also have to roll out my own
"contains"
(e.g., `element in set`) function.

I expect and hope there's a pythonic way to do this. Does it exist?

Thanks in advance!
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Re: Status of Python threading support (GIL removal)?

[Christian Heimes]

OdarR wrote:
> I don't see such improvement in the Python library, or maybe you can
> indicate us some meaningfull example...?
> 
> I currently only use CPython, with PIL, Reportlab...etc.
> I don't see improvement on a Core2duo CPU and Python. How to proceed
> (following what you wrote) ?

I've seen a single Python process using the full capacity of up to 8
CPUs. The application is making heavy use of lxml for large XSL
transformations, a database adapter and my own image processing library
based upon FreeImage.

Of course both lxml and my library are written with the GIL in mind.
They release the GIL around every call to C libraries that don't touch
Python objects. PIL releases the lock around ops as well (although it
took me a while to figure it out because PIL uses its own API instead of
the standard macros). reportlab has some optional C libraries that
increase the speed, too. Are you using them?

By the way threads are evil
(http://www.eecs.berkeley.edu/Pubs/TechRpts/2006/EECS-2006-1.pdf) and
not *the* answer to concurrency.

Christian

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Re: Status of Python threading support (GIL removal)?

[Carl Banks]

On Jun 19, 6:53 am, Ben Charrow  wrote:
> Jure Erznožnik wrote:
> > See here for introduction:
> >http://groups.google.si/group/comp.lang.python/browse_thread/thread/3...
>
> > Digging through my problem, I discovered Python isn't exactly thread
> > safe and to solve the issue, there's this Global Interpreter Lock
> > (GIL) in place.
> > Effectively, this causes the interpreter to utilize one core when
> > threading is not used and .95 of a core when threading is utilized.
>
> > Is there any work in progess on core Python modules that will
> > permanently resolve this issue?
> > Is there any other way to work around the issue aside from forking new
> > processes or using something else?
>
> There is a group of people working on an alternative implementation to Python
> that, among other things, will not have a 
> GIL:http://code.google.com/p/unladen-swallow/


That's not a foregone conclusion.  Well it's not a foregone conclusion
that unladen-swallow will succeed at all, but even if it does they
only say they intend to remove the GIL, not that they necessarily
will.

The GIL actually "solves" two problems: the overhead of synchronizing
reference counts, and the difficulty of writing threaded extensions.
The unladen-swallow team only address the first problem in their
plans.  So, even if they do remove the GIL,  I doubt GvR will allow it
to be merged back into CPython unless makes extensions are just as
easy to write.  That is something I have serious doubts they can pull
off.

Which means a GIL-less unladen-swallow is likely to end being another
fork like IronPython and Jython.  Those projects already have no GIL.


Carl Banks
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Re: Measuring Fractal Dimension ?

[Charles Yeomans]

On Jun 19, 2009, at 2:43 PM, David C. Ullrich wrote:


Evidently my posts are appearing, since I see replies.
I guess the question of why I don't see the posts themselves
\is ot here...

On Thu, 18 Jun 2009 17:01:12 -0700 (PDT), Mark Dickinson
 wrote:

On Jun 18, 7:26 pm, David C. Ullrich   
wrote:

On Wed, 17 Jun 2009 08:18:52 -0700 (PDT), Mark Dickinson

Right.  Or rather, you treat it as the image of such a function,
if you're being careful to distinguish the curve (a subset
of R^2) from its parametrization (a continuous function
R -> R**2).  It's the parametrization that's uniformly
continuous, not the curve,


Again, it doesn't really matter, but since you use the phrase
"if you're being careful": In fact what you say is exactly
backwards - if you're being careful that subset of the plane
is _not_ a curve (it's sometimes called the "trace" of the curve".


Darn.  So I've been getting it wrong all this time.  Oh well,
at least I'm not alone:

"De?nition 1. A simple closed curve J, also called a
Jordan curve, is the image of a continuous one-to-one
function from R/Z to R2. [...]"

- Tom Hales, in 'Jordan's Proof of the Jordan Curve Theorem'.

"We say that Gamma is a curve if it is the image in
the plane or in space of an interval [a, b] of real
numbers of a continuous function gamma."

- Claude Tricot, 'Curves and Fractal Dimension' (Springer, 1995).

Perhaps your definition of curve isn't as universal or
'official' as you seem to think it is?


Perhaps not. I'm very surprised to see those definitions; I've
been a mathematician for 25 years and I've never seen a
curve defined a subset of the plane.



I have.




Hmm. You left out a bit in the first definition you cite:

"A simple closed curve J, also called a Jordan curve, is the image
of a continuous one-to-one function from R/Z to R2. We assume that
each curve
comes with a fixed parametrization phi_J : R/Z ->¨ J. We call t in R/Z
the time
parameter. By abuse of notation, we write J(t) in R2 instead of phi_j
(t), using the
same notation for the function phi_J and its image J."


Close to sounding like he can't decide whether J is a set or a
function...


On the contrary, I find this definition to be written with some care.


 Then later in the same paper

"Definition 2. A polygon is a Jordan curve that is a subset of a
finite union of
lines. A polygonal path is a continuous function P : [0, 1] ->¨ R2
that is a subset of
a finite union of lines. It is a polygonal arc, if it is 1 . 1."



These are a bit too casual for me as well...


By that definition a polygonal path is not a curve.

Worse: A polygonal path is a function from [0,1] to R^2
_that is a subset of a finite union of lines_. There's no
such thing - the _image_ of such a function can be a
subset of a finite union of lines.

Not that it matters, but his defintion of "polygonal path"
is, _if_ we're being very careful, self-contradictory.
So I don't think we can count that paper as a suitable
reference for what the _standard_ definitions are;
the standard definitions are not self-contradictory this way.



Charles Yeomans
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timeit and __future__

[Karl Chen]

I wanted to time something that uses with_statement, in python2.5.
Importing __future__ in the statement or the setup doesn't work
since it's not the beginning of the code being compiled.  Other
than using a separate module, I could only come up with this:

timeit.template = 'from __future__ import with_statement\n' + 
timeit.template

timeit should directly support importing __future__ stuff...

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dynamically associate radio buttons with droplists

[Leo Brugud]

Hi Folks,

Not being very familiar with python, nor with cgi/http,  I intend to
have 3 of buttons in a webpage, each of them is associate with a file
(so I have 3 files, too)

What I would like to have is, when users choose a button, the droplist
update automatically to load the contents of the associated file.

Can someone educate me the approach of this?

Thanks
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Re: Rich comparison methods don't work in sets?

[Matthew Wilson]

On Fri 19 Jun 2009 03:02:44 PM EDT, Gustavo Narea wrote:
> Hello, everyone.
>
> I've noticed that if I have a class with so-called "rich comparison"
> methods
> (__eq__, __ne__, etc.), when its instances are included in a set,
> set.__contains__/__eq__ won't call the .__eq__ method of the elements
> and thus
> the code below:
> """
> obj1 = RichComparisonClass()
> obj2 = RichComparisonClass()

What does 

>>> obj1 is obj2

return? I don't know anything about set internals.

Matt
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Re: n00b confusion re: local variable referenced before assignment error

[Dave Angel]

Wells Oliver wrote:

Writing a class which essentially spiders a site and saves the files
locally. On a URLError exception, it sleeps for a second and tries again (on
404 it just moves on). The relevant bit of code, including the offending
method:

class Handler(threading.Thread):
def __init__(self, url):
threading.Thread.__init__(self)
self.url = url

def save(self, uri, location):
try:
handler = urllib2.urlopen(uri)
except urllib2.HTTPError, e:
if e.code == 404:
return
else:
print "retrying %s (HTTPError)" % uri
time.sleep(1)
self.save(uri, location)
except urllib2.URLError, e:
print "retrying %s" % uri
time.sleep(1)
self.save(uri, location)

if not os.path.exists(os.path.dirname(location)):
os.makedirs(os.path.dirname(location))

file = open(location, "w")
file.write(handler.read())
file.close()

...

But what I am seeing is that after a retry (on catching a URLError
exception), I see bunches of "UnboundLocalError: local variable 'handler'
referenced before assignment" errors on line 38, which is the
"file.write(handler.read())" line..

What gives?

  
Your save() method is recursive in the case of that error, which is a 
poor excuse for what should have been a loop.  You should have some 
retry depth check, just in case you get hundreds of such errors on the 
same site.


But ignoring that issue, the specific symptom is caused when returning 
from the recursive call.  You still fall through to the end of your 
outer method call, and try to write stuff from that handler (also wiping 
out the file "location" in the process).  Without a handler, that causes 
an exception.  So you should follow those calls to self.save() with 
return's.


Much better would be to write a loop in the first place, and break out 
of the loop when you succeed.  Then the flow is much easier to follow, 
and you can easily avoid the risk of looping forever, nor of running out 
of stack space.


Something like (untested):

   def save(self, uri, location):
   for tries in xrange(10):#try up to 10 times
   try:
   handler = urllib2.urlopen(uri)
   except urllib2.HTTPError, e:
   if e.code == 404:
   break
   else:
   print "retrying %s (HTTPError)" % uri
   time.sleep(1)
   continue
   except urllib2.URLError, e:
   print "retrying %s" % uri
   time.sleep(1)
   continue

   if not os.path.exists(os.path.dirname(location)):
   os.makedirs(os.path.dirname(location))

   file = open(location, "w")
   file.write(handler.read())
   file.close()
   break

Other refinements are possible, of course.  For example, if you have any 
cleanup code at the end you may need an additional flag variable to tell 
whether you've succeeded or not.


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Re: Is this pylint error message valid or silly?

[nn]

On Jun 18, 8:56 pm, Matthew Wilson  wrote:
> Here's the code that I'm feeding to pylint:
>
>     $ cat f.py
>     from datetime import datetime
>
>     def f(c="today"):
>
>         if c == "today":
>                     c = datetime.today()
>
>         return c.date()
>
> And here's what pylint says:
>
>     $ pylint -e f.py
>     No config file found, using default configuration
>     * Module f
>     E: 10:f: Instance of 'str' has no 'date' member (but some types could
>     not be inferred)
>
> Is this a valid error message?  Is the code above bad?  If so, what is
> the right way?
>
> I changed from using a string as the default to None, and then pylint
> didn't mind:
>
>     $ cat f.py
>     from datetime import datetime
>
>     def f(c=None):
>
>         if c is None:
>                     c = datetime.today()
>
>         return c.date()
>
>     $ pylint -e f.py
>     No config file found, using default configuration
>
> I don't see any difference between using a string vs None.  Both are
> immutable.  I find the string much more informative, since I can write
> out what I want.
>
> Looking for comments.
>
> Matt

>>> def midnight_next_day(initial_time=None):

 if initial_time == "use today's  date":
initial_time = datetime.now()

 return initial_time.date() + timedelta(days=1)

>>> midnight_next_day()

Traceback (most recent call last):
  File "", line 1, in 
midnight_next_day()
  File "", line 6, in midnight_next_day
return initial_time.date() + timedelta(days=1)
AttributeError: 'NoneType' object has no attribute 'date'
>>>
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Re: Rich comparison methods don't work in sets?

[Peter Otten]

Gustavo Narea wrote:

> I've noticed that if I have a class with so-called "rich comparison"
> methods
> (__eq__, __ne__, etc.), when its instances are included in a set,
> set.__contains__/__eq__ won't call the .__eq__ method of the elements
> and thus
> the code below:
> """
> obj1 = RichComparisonClass()

How is RichComparisonClass implemented? Did you provide a __hash__() method 
such that obj1 == obj2 implies hash(obj1) == hash(obj2)? This is necessary 
for instances of the class to work properly with sets and dicts.

Peter

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Re: Measuring Fractal Dimension ?

[Mark Dickinson]

On Jun 19, 7:43 pm, David C. Ullrich  wrote:
> Evidently my posts are appearing, since I see replies.
> I guess the question of why I don't see the posts themselves
> \is ot here...

Judging by this thread, I'm not sure that much is off-topic
here.  :-)

> Perhaps not. I'm very surprised to see those definitions; I've
> been a mathematician for 25 years and I've never seen a
> curve defined a subset of the plane.

That in turn surprises me.  I've taught multivariable
calculus courses from at least three different texts
in three different US universities, and as far as I
recall a 'curve' was always thought of as a subset of
R^2 or R^3 in those courses (though not always with
explicit definitions, since that would be too much
to hope for with that sort of text).  Here's Stewart's
'Calculus', p658:

"Examples 2 and 3 show that different sets of parametric
equations can represent the same curve.  Thus we
distinguish between a *curve*, which is a set of points,
and a *parametric curve*, in which the points are
traced in a particular way."

Again as far as I remember, the rest of the language
in those courses (e.g., 'level curve', 'curve as the
intersection of two surfaces') involves thinking
of curves as subsets of R^2 or R^3.  Certainly
I'll agree that it's then necessary to parameterize
the curve before being able to do anything useful
with it.

[Standard question when teaching multivariable
calculus:  "Okay, so we've got a curve.  What's
the first thing we do with it?"  Answer, shouted
out from all the (awake) students: "PARAMETERIZE IT!"
(And then calculate its length/integrate the
given vector field along it/etc.)
Those were the days...]

A Google Books search even turned up some complex
analysis texts where the word 'curve' is used to
mean a subset of the plane;  check out
the book by Ian Stewart and David Orme Tall,
'Complex Analysis: a Hitchhiker's Guide to the
Plane':  they distinguish 'curves' (subset of the
complex plane) from 'paths' (functions from a
closed bounded interval to the complex plane).

> "Definition 2. A polygon is a Jordan curve that is a subset of a
> finite union of
> lines. A polygonal path is a continuous function P : [0, 1] ->¨ R2
> that is a subset of
> a finite union of lines. It is a polygonal arc, if it is 1 . 1."
>
> By that definition a polygonal path is not a curve.

Right.  I'm much more willing to accept 'path' as standard
terminology for a function [a, b] -> (insert_favourite_space_here).

> Not that it matters, but his defintion of "polygonal path"
> is, _if_ we're being very careful, self-contradictory.

Agreed.  Surprising, coming from Hales; he must surely rank
amongst the more careful mathematicians out there.

> So I don't think we can count that paper as a suitable
> reference for what the _standard_ definitions are;
> the standard definitions are not self-contradictory this way.

I just don't believe there's any such thing as
'the standard definition' of a curve.  I'm happy
to believe that in complex analysis and differential
geometry it's common to define a curve to be a
function.  But in general I'd suggest that it's one
of those terms that largely depends on context, and
should be defined clearly when it's not totally
obvious from the context which definition is
intended.  For example, for me, more often than not,
a curve is a 1-dimensional scheme over a field k
(usually *not* algebraically closed), that's at
least some of {geometrically reduced, geometrically
irreducible, proper, smooth}.  That's a far cry either
from a subset of an affine space or from a
parametrization by an interval.

> Then the second definition you cite: Amazon says the
> prerequisites are two years of calculus. The stanard
> meaning of log is log base e, even though means
> log base 10 in calculus.

Sorry, I've lost context for this comment.  Why
are logs relevant?  (I'm very well aware of the
debates over the meaning of log, having frequently
had to help students 'unlearn' their "log=log10"
mindset when starting a first post-calculus course).

Mark
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Re: Is this pylint error message valid or silly?

[nn]

On Jun 18, 8:56 pm, Matthew Wilson  wrote:
> Here's the code that I'm feeding to pylint:
>
>     $ cat f.py
>     from datetime import datetime
>
>     def f(c="today"):
>
>         if c == "today":
>                     c = datetime.today()
>
>         return c.date()
>
> And here's what pylint says:
>
>     $ pylint -e f.py
>     No config file found, using default configuration
>     * Module f
>     E: 10:f: Instance of 'str' has no 'date' member (but some types could
>     not be inferred)
>
> Is this a valid error message?  Is the code above bad?  If so, what is
> the right way?
>
> I changed from using a string as the default to None, and then pylint
> didn't mind:
>
>     $ cat f.py
>     from datetime import datetime
>
>     def f(c=None):
>
>         if c is None:
>                     c = datetime.today()
>
>         return c.date()
>
>     $ pylint -e f.py
>     No config file found, using default configuration
>
> I don't see any difference between using a string vs None.  Both are
> immutable.  I find the string much more informative, since I can write
> out what I want.
>
> Looking for comments.
>
> Matt

>>> def midnight_next_day(initial_time="use today's date"):

 if initial_time == "use today's  date":
initial_time = datetime.now()

 return initial_time.date() + timedelta(days=1)

>>> midnight_next_day()

Traceback (most recent call last):
  File "", line 1, in 
midnight_next_day()
  File "", line 6, in midnight_next_day
return initial_time.date() + timedelta(days=1)
AttributeError: 'str' object has no attribute 'date'
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Re: Status of Python threading support (GIL removal)?

[Carl Banks]

On Jun 19, 11:08 am, OdarR  wrote:
> On 19 juin, 19:13, s...@pobox.com wrote:
>
> >     Olivier> what do you mean ?
>
> >     Olivier> Cpython can't benefit from multi-core without multiple
> >     Olivier> processes.
>
> > It can, precisely as Martin indicated.  Only one thread at a time can hold
> > the GIL.  That doesn't mean that multiple threads can't execute.  Suppose
>
> I don't say multiple threads can't execute(?).
> I say that with the Python library, I don't see (yet) benefit with
> multiple threads *on* multiple CPU/core.


He's saying that if your code involves extensions written in C that
release the GIL, the C thread can run on a different core than the
Python-thread at the same time.  The GIL is only required for Python
code, and C code that uses the Python API.  C code that spends a big
hunk of time not using any Python API (like, as Skip pointed out, a
matrix multiply) can release the GIL and the thread can run on a
different core at the same time.

I always found to be a *terribly* weak rationalization.  The fact is,
few Python developers can take much advantage of this.

(Note: I'm not talking about releasing the GIL for I/O operations,
it's not the same thing.  I'm talking about the ability to run
computations on multiple cores at the same time, not to block in 50
threads at the same time.  Multiple cores aren't going to help that
much in the latter case.)

I wish Pythonistas would be more willing to acknowledge the (few)
drawbacks of the language (or implementation, in this case) instead of
all this rationalization.  It's like people here in Los Angeles who
complain about overcast days.  What, 330 days of sunshine not enough?
Jesus.  I wish people would just say, "This is a limitation of
CPython.  There are reasons why it's there, and it helps some people,
but unfortunately it has drawbacks for others", instead of the typical
"all u hav 2 do is rite it in C LOL".


Carl Banks
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Re: fastest native python database?

[Aaron Brady]

On Jun 17, 8:28 pm, per  wrote:
> hi all,
>
> i'm looking for a native python package to run a very simple data
> base. i was originally using cpickle with dictionaries for my problem,
> but i was making dictionaries out of very large text files (around
> 1000MB in size) and pickling was simply too slow.
>
> i am not looking for fancy SQL operations, just very simple data base
> operations (doesn't have to be SQL style) and my preference is for a
> module that just needs python and doesn't require me to run a separate
> data base like Sybase or MySQL.
>
> does anyone have any recommendations? the only candidates i've seen
> are snaklesql and buzhug... any thoughts/benchmarks on these?
>
> any info on this would be greatly appreciated. thank you

I have one or two.  If the objects you're pickling are all
dictionaries, you could store file names in a master 'shelve' object,
and nested data in the corresponding files.

Otherwise, it may be pretty cheap to write the operations by hand
using ctypes if you only need a few, though that can get precarious
quickly.  Just like life, huh?

Lastly, the 'sqlite3' module's bark is worse than its byte.
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Re: Is this pylint error message valid or silly?

[nn]

On Jun 18, 8:56 pm, Matthew Wilson  wrote:
> Here's the code that I'm feeding to pylint:
>
>     $ cat f.py
>     from datetime import datetime
>
>     def f(c="today"):
>
>         if c == "today":
>                     c = datetime.today()
>
>         return c.date()
>
> And here's what pylint says:
>
>     $ pylint -e f.py
>     No config file found, using default configuration
>     * Module f
>     E: 10:f: Instance of 'str' has no 'date' member (but some types could
>     not be inferred)
>
> Is this a valid error message?  Is the code above bad?  If so, what is
> the right way?
>
> I changed from using a string as the default to None, and then pylint
> didn't mind:
>
>     $ cat f.py
>     from datetime import datetime
>
>     def f(c=None):
>
>         if c is None:
>                     c = datetime.today()
>
>         return c.date()
>
>     $ pylint -e f.py
>     No config file found, using default configuration
>
> I don't see any difference between using a string vs None.  Both are
> immutable.  I find the string much more informative, since I can write
> out what I want.
>
> Looking for comments.
>
> Matt

This is a limitation of static type checking and Pylint is a (limited)
static type checker for Python. A language with static type checking
would not have even allowed you to compile this. A static type
checkers sees this:

def midnight_next_day(initial_time [string or in python whatever gets
passed(T)]):

 if initial_time [string (or T)]== [(some constant) string]:
initial_time [datetime] = datetime.now()
 {implied else:
 initial_time [string or (T)] }

 return initial_time[could be either datetime or string (oops
string does not have date()) pylint doesn’t check for T].date() +
timedelta(days=1)

or this:

def midnight_next_day(initial_time [None object or (T)]):

 if initial_time [None object or (T)]== [None object]:
initial_time [type datetime] = datetime.now()
 {implied else:
 initial_time [T] }

 return initial_time[datetime (pylint doesn’t check for T)].date()
+ timedelta(days=1)
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Re: CAD file format specifications?

[Anthra Norell]

Dennis Lee Bieber wrote:

On Thu, 18 Jun 2009 13:39:28 +0200, Anthra Norell
 declaimed the following in
gmane.comp.python.general:


  
utility. So, my question is: How do I convert a bunch of 
three-dimensional coordinates defining lines into a file format Sketch 
Up can read (skp, dwg, dxf, 3ds, ddf or dem)?




Most CAD type data files are highly structured -- and the formats
may be under company control...

http://en.wikipedia.org/wiki/USGS_DEM
http://rockyweb.cr.usgs.gov/nmpstds/acrodocs/dem/2DEM0198.PDF

http://www.martinreddy.net/gfx/3d/3DS.spec
  

Dennis, norseman,
  Thanks for your suggestions. First thing I'm trying to write a DXF 
converter using norseman's excellent documentation. It seems I only need 
a simple subset of the DXF format (Entities). When I'm done I shall take 
a close look at the links above. So, thanks again.


Frederic


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Re: multiprocessing and process run time

[Piet van Oostrum]

> Thomas Robitaille  (TR) wrote:

>TR> Hi,

>TR> I'm making use of the multiprocessing module, and I was wondering if there
>TR> is an easy way to find out how long a given process has been running for.
>TR> For example, if I do

>TR> import multiprocessing as mp
>TR> import time

>TR> def time_waster():
>TR> time.sleep(1000)

>TR> p = mp.Process(target=time_waster)

>TR> p.start()

>TR> Is there a way that I can then find how long p has been running for? I
>TR> figured I can use p.pid to get the PID of the process, but I'm not sure
>TR> where to go from there. Is there an easy way to do this?

You could look at the psutil module: http://code.google.com/p/psutil/
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URL: http://pietvanoostrum.com [PGP 8DAE142BE17999C4]
Private email: p...@vanoostrum.org
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Re: Rich comparison methods don't work in sets?

[Chris Rebert]

On Fri, Jun 19, 2009 at 12:02 PM, Gustavo Narea wrote:
> Hello, everyone.
>
> I've noticed that if I have a class with so-called "rich comparison"
> methods
> (__eq__, __ne__, etc.), when its instances are included in a set,
> set.__contains__/__eq__ won't call the .__eq__ method of the elements
> and thus
> the code below:
> """
> obj1 = RichComparisonClass()
> obj2 = RichComparisonClass()
>
> set1 = set([obj1])
> set2 = set([obj2])
>
> if obj1 == obj2:
>    print "Objects 1 and 2 are equivalent"
> else:
>    print "Objects 1 and 2 aren't equivalent"
>
> if set1 == set2:
>    print "Sets 1 and 2 are equivalent"
> else:
>    print "Sets 1 and 2 aren't equivalent"
> """
>
> Would output:
> """
> Objects 1 and 2 are equivalent
> Sets 1 and 2 aren't equivalent
> """
>
> instead of:
> """
> Objects 1 and 2 are equivalent
> Sets 1 and 2 are equivalent
> """
>
> How can I work around this? The only solution that comes to my mind is

Note that sets are dict-based and thus use hash tables internally.
Thus, you must implement a sensible __hash__ method.
The default __hash__ provided by class `object` uses the object ID for the hash.

Since id(x) == id(y)  iff  x is y, and
hash(x) != hash(y) implies x != y,
If you don't implement __hash__, object's implementation causes every
distinct object of your type to be considered unequal a priori, so it
doesn't bother to check any further by calling the comparison methods.

Cheers,
Chris
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Re: Tutorial on working with Excel files in Python (without COM and crossplatform!) at EuroPython 2009

[Jeremiah Jester]

Chris,
Do you have any online tutorial for this topic? 
Thanks,
JJ

On Thu, 2009-06-18 at 08:38 -0700, Chris Withers wrote:
> Hi All,
> 
> Too many people in the Python community *still* think the only way to
> work with Excel files in Python is using COM on Windows.
> 
> To try and correct this, I'm giving a tutorial at this year's
> EuroPython
> conference in Birmingham, UK on Monday, 29th June that will cover
> working with Excel files in Python using the pure-python libraries
> xlrd,
> xlwt and xlutils.
> 
> I'll be looking to cover:
> 
> - Reading Excel Files
> 
>Including extracting all the data types, formatting and working
> with
>large files.
> 
> - Writing Excel Files
> 
>Including formatting, many of the useful frilly extras and writing
>large excel files.
> 
> - Modifying and Filtering Excel Files
> 
>A run through of taking existing Excel files and modifying them in
>various ways.
> 
> - Workshop for your problems
> 
>I'm hoping anyone who attends will get a lot out of this! If you're
>planning on attending and have a particular problem you'd like to
> work
>on in this part of the tutorial, please drop me an email and I'll
> try
>and make sure I come prepared!
> 
> All you need for the tutorial is a working knowledge of Excel and
> Python, with a laptop as an added benefit, and to be at EuroPython
> this
> year:
> 
> http://www.europython.eu/
> 
> I look forward to seeing you all there!
> 
> Chris
> 
> --
> Simplistix - Content Management, Zope & Python Consulting
> - http://www.simplistix.co.uk
> 
> 
> --
> http://mail.python.org/mailman/listinfo/python-announce-list
> 
> Support the Python Software Foundation:
> http://www.python.org/psf/donations.html
> 
> 
> 


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