Re: elementtree

[Nadia Johnson]

On Aug 24, 7:29 pm, Dave Angel  wrote:
> Stefan Behnel wrote:
> > Hi,
>
> > elsa wrote:
>
> >> I know how to turn HTML into an ElementTree object
>
> > I don't. ;)
>
> > ElementTree doesn't have an HTML parser, so what do you use for parsing?
>
> >> but I don't know
> >> how to then view the structure of this object. Is there a method or
> >> module that you can give an ElementTree object to, and it returns some
> >> kind of graphical or printed representation of the tree? Otherwise, if
> >> you can't see you're tree's structure, how do you know what is a
> >> sensible way of iterating over the tree to access the info you need?
>
> > ElementTree has a tostring() method that returns a string. To get a pretty
> > printed representation, you can use the indent() function from this recipe:
>
> >http://effbot.org/zone/element-lib.htm#prettyprint
>
> > Stefan
>
> Perhaps the OP was referring to XHTML, which should be eligible for
> ElementTree.  But could you tell me whether ElementTree is at all
> tolerant of malformed XML?   Most HTML and XHTML I encounter in the wild
> is so  buggy it's amazing it all works at all.
>
> DaveA

I used elementtidy, also available from effbot
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Re: Python memory management <-> virtualized server environments

[gravityzoo-dmo]

On 24 aug, 20:35, "Martin P. Hellwig" 
wrote:
> gravityzoo-dmo wrote:
> > Hello everyone,
>
> > I was wondering if anyone here has had any experience in running
> > Python in a virtualized server environment?
> > The reason I'm asking is the recent thing I noticed when running my
> > server application (written in Python + Twisted);
> > The memory of the server application seems to only grow, and not give
> > back memory space to the OS. I realize that this won't be a problem on
> > a single physical server, but I'm curious of the effect this behaviour
> > has on a virtualized environment.
> > Could anyone provide me with a little more insight please?
> > Thanks in advance!
>
> > Dirk
>
> Might help if you say which version of Python you are running, although
> I'm not a memory expert I do know there have been some changes between
> the versions.
>
> --
> MPHhttp://blog.dcuktec.com
> 'If consumed, best digested with added seasoning to own preference.'

Hi, I'm sorry, I forgot to post the version indeed.

The Python version I'm running is 2.5.2 (r252:60911, January 4 2009)
The Twisted version I'm running is 8.2.0, and I'm using the EPOLL-
Reactor (don't know if that matters)
The OS I'm running on is Debian version 2.6.26-2-686 (i686 GNU/Linux)

Is that enough info?

Best regards,
Dirk
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Re: Putting together a larger matrix from smaller matrices

[Peter Otten]

Matjaz Bezovnik wrote:

> This is something which is done often in FEM methods, and the alike.
> 
> I have matrix A of 3x3 elements, and B, of the same number of
> elements, 3x3.
> 
> What would be the most obvious way to assemble a matrix which:
> a11 a12 a13
> a21 a22 a23
> a31 a32 a33+b11 b12 b13
>   b21 b22 b23
>   b31 b32 b33
> 
> (the missing elements = zero)
> 
> (you see the pattern - if there was a third matrix C, it would
> "connect" to b33 on the main diagonal)

Unless there is a dedicated function:

partial = [...] # list of matrices of shape NxN

N = partial[0].shape[0]
width = N*len(partial)
b = numpy.zeros((width, width))

off = 0
for m in partial:
b[off:off+N, off:off+N] = m
off += N
print b

Peter


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Re: Python memory management <-> virtualized server environments

[Martin P. Hellwig]

gravityzoo-dmo wrote:

On 24 aug, 20:35, "Martin P. Hellwig" 
wrote:

gravityzoo-dmo wrote:

Hello everyone,
I was wondering if anyone here has had any experience in running
Python in a virtualized server environment?
The reason I'm asking is the recent thing I noticed when running my
server application (written in Python + Twisted);
The memory of the server application seems to only grow, and not give
back memory space to the OS. I realize that this won't be a problem on
a single physical server, but I'm curious of the effect this behaviour
has on a virtualized environment.
Could anyone provide me with a little more insight please?
Thanks in advance!
Dirk

Might help if you say which version of Python you are running, although
I'm not a memory expert I do know there have been some changes between
the versions.

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


Hi, I'm sorry, I forgot to post the version indeed.

The Python version I'm running is 2.5.2 (r252:60911, January 4 2009)
The Twisted version I'm running is 8.2.0, and I'm using the EPOLL-
Reactor (don't know if that matters)
The OS I'm running on is Debian version 2.6.26-2-686 (i686 GNU/Linux)

Is that enough info?

Best regards,
Dirk



According to Python 2.6 release document:
"To reduce memory usage, the garbage collector will now clear internal 
free lists when garbage-collecting the highest generation of objects. 
This may return memory to the operating system sooner."


Which might apply to your situation, but to be really sure you can only 
try it out :-)


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

[Pierre]

Hello,

I'm to plot some results but it doesn't work.
I got this error :

/usr/local/libre_rep/python-2.6.1/RHEL_5__x86_64/lib/python2.6/site-
packages/matplotlib/backends/__init__.py:41: UserWarning:
Your currently selected backend, 'agg' does not support show().
Please select a GUI backend in your matplotlibrc file ('/usr/local/
libre_rep/python-2.6.1/RHEL_5__x86_64/lib/python2.6/site-packages/
matplotlib/mpldata/matplotlibrc')
or with matplotlib.use()

Any idea to fix it ?

Thanks
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Re: Numeric literals in other than base 10 - was Annoying octal notation

[James Harris]

On 25 Aug, 01:25, Steven D'Aprano  wrote:

> On Mon, 24 Aug 2009 16:23:06 -0700, James Harris wrote:

> > Sure but while I wouldn't normally want to type something as obscure as
> > 32"rst" into a file of data I might want to type 0xff00 or similar. That
> > is far clearer than 65280 in some cases.
>
> > My point was that int('ff00', 16) is OK for the programmer but cannot be
> > used generally as it includes a function call.
>
> No, it's the other way around. If you have *data*, whether entered at run
> time by the user or read from a file, you can easily pass it to a
> function to convert to an int. (In fact you have to do this anyway,
> because the data will be a string and you need an int.)
>
> If you want your data file to have values entered in hex, or oct, or even

You are looking at this the other way round from me and I'll explain
why I think this is important. I'm not talking about the *programmer*
prescribing how the user should enter the data but the *user* being
able to choose to prepare the data in a certain format - the format
which makes sense for the data being entered. Your way only works if
those fields in every row have the same format. That may be the case
sometimes but is not general.


> unary (1=one, 11=two, 111=three, =four...) you can. There's no need
> to have the user enter int('ff00', 16) to get hex, just have them enter
> ff00.
>
> But when writing *code*, you want syntax which will accept integers in
> the most common bases (decimal, a distant second hex, an even more
> distant third octal, and way out on the horizon binary) without the
> runtime cost of a function call.

Be careful! When designing a language feature don't be too ready to
*tell* the users of that language what restrictions they want. Just
because the designer wants features with a certain frequency does not
mean that all users will have the same priorities. (If it is
impossible or unreasonable to support a feature then by all means
don't support it. But don't decide up-front before examining the
options that something in not personally appealing.)

James
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Re: Protecting against callbacks queuing up?

[Hendrik van Rooyen]

On Monday 24 August 2009 17:32:23 Esben von Buchwald wrote:
> Hendrik van Rooyen wrote:

8< -- some stuff about an "after" call --
>
> I'm new to python, what is an after function and an after call? Couldn't
> find excact answer on google...? Do you have a link to some docs?

The after call is common in GUI stuff.

Here is a link to nice Tkinter manual - it is the first link if you google 
for:   tkinter "new mexico tech" shipman

www.nmt.edu/tcc/help/pubs/tkinter/

What after does is that it is like a normal call, except that it is not done 
immediately, but after some settable time, hence the "after".

- Hendrik
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os.popen output different from native shell output

[nickname]

Hi all,
   I am a relative newbie to python, I am using os.popen to run an
ls command. The output that I get using the read() function is
different in look and feel from when I run the ls command natively
from the shell (not via python). I display the ouput via python by
using the print function on the variable that accepts the os.popen
().read() function.

For example:

output from native shell (as seen on the bash shell)

file1 file2 dir1(highlighted in blue color)
file3longnamewhichwillcausenextfiletoappearonnextline

file 4

output from python (as seen on the bash shell)

file1
file2
dir1 (no blue color)
file3longnamewhichwillcausenextfiletoappearonnextline
file4

Is there an easy way to "mirror" the output. When python displays the
output, how can it tell the bash shell that some of the entries are
directories and they should appear blue on the bash shell, and that
everything should not be appearing on 1 column only.

Thanks for any pointers.
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Re: os.popen output different from native shell output

[Chris Rebert]

On Tue, Aug 25, 2009 at 1:36 AM, nickname wrote:
> Hi all,
>       I am a relative newbie to python, I am using os.popen to run an
> ls command. The output that I get using the read() function is
> different in look and feel from when I run the ls command natively
> from the shell (not via python). I display the ouput via python by
> using the print function on the variable that accepts the os.popen
> ().read() function.
>
> For example:
>
> output from native shell (as seen on the bash shell)
>
> file1 file2 dir1(highlighted in blue color)
> file3longnamewhichwillcausenextfiletoappearonnextline
>
> file 4
>
> output from python (as seen on the bash shell)
>
> file1
> file2
> dir1 (no blue color)
> file3longnamewhichwillcausenextfiletoappearonnextline
> file4
>
> Is there an easy way to "mirror" the output. When python displays the
> output, how can it tell the bash shell that some of the entries are
> directories and they should appear blue on the bash shell, and that
> everything should not be appearing on 1 column only.

I would assume the difference is caused by `ls` changing behavior (for
example, enabling/disabling colorization) based on whether its output
is going to a terminal or a pipe.

Is there a reason you can't use os.listdir() instead of running ls?:
http://docs.python.org/library/os.html#os.listdir

For the colorization, google for "ANSI color escape sequences"

Cheers,
Chris
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Re: Questions on XML

[SUBHABRATA BANERJEE]

I was trying this. Looks perfectly fine. There must be something really
wrong. If you can reinstall Python 2.5.
>>> a1=raw_input("String")
Stringআম

On Mon, Aug 24, 2009 at 12:18 AM, Rami Chowdhury
wrote:

> My problem is with IDLE on Windows. When I try to type Bangla directly into
> the IDLE window I only get '?' characters, and repr() fails with a
> UnicodeDecodeError. I expect, though, that that's because of my specific
> installation / Windows issues, as it works fine on Fedora 10...
>
> > I do not get any problem in processing Hindi or Bangla or any Indian
> > language in Python it is perfectly fine.
> I have no problems either -- my issues are with IDLE, and only on Windows.
>
> 
> Rami Chowdhury
> "Strangers are just friends who haven't had enough gin." -- Howdle's Saying
> 408-597-7068 (US) / 07875-841-046 (UK) / 0189-245544 (BD)
>
>  On Saturday 22 August 2009 13:27:02 SUBHABRATA BANERJEE wrote:
> > Should I help you? If you answered my questions I am differing from your
> > view I do not get any problem in processing Hindi or Bangla or any Indian
> > language in Python it is perfectly fine.
> > Best Regards,
> > Subhabrata.
> >
> > On Sat, Aug 22, 2009 at 9:48 AM, Rami Chowdhury
> wrote:
> > > I am using primarily UTF-8 based strings, like Hindi or Bengali. Can I
> > >
> > >> use Python to help me in this regard?
> > >
> > > I can say from experience that Python on Windows (at least, Python 2.5
> on
> > > 32-bit Vista) works perfectly well with UTF-8 files containing Bangla.
> I
> > > have had trouble with working with the data in IDLE, however, which
> seems
> > > to prefer ASCII by default.
> > >
> > > -
> > > Rami Chowdhury
> > > "Never assume malice when stupidity will suffice." -- Hanlon's Razor
> > > 408-597-7068 (US) / 07875-841-046 (UK) / 0189-245544 (BD)
> > >
> > >
> > >
> > >
> > >
> > > On Aug 21, 2009, at 19:15 , joy99 wrote:
> > >
> > >   Dear Group,
> > >
> > >> I like to convert some simple strings of natural language to XML. May
> > >> I use Python to do this? If any one can help me, on this.
> > >>
> > >> I am using primarily UTF-8 based strings, like Hindi or Bengali. Can I
> > >> use Python to help me in this regard?
> > >>
> > >> How can I learn good XML aspects of Python. If any one can kindly name
> > >> me a book or URL.
> > >>
> > >> I am using Python2.6 on Windows XP with IDLE as GUI.
> > >>
> > >> Best Regards,
> > >> Subhabrata.
> > >> --
> > >> http://mail.python.org/mailman/listinfo/python-list
>
>
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Re: matplotlib / backend

[baloan]

On Aug 25, 10:12 am, Pierre  wrote:
> Hello,
>
> I'm to plot some results but it doesn't work.
> I got this error :
>
> /usr/local/libre_rep/python-2.6.1/RHEL_5__x86_64/lib/python2.6/site-
> packages/matplotlib/backends/__init__.py:41: UserWarning:
> Your currently selected backend, 'agg' does not support show().
> Please select a GUI backend in your matplotlibrc file ('/usr/local/
> libre_rep/python-2.6.1/RHEL_5__x86_64/lib/python2.6/site-packages/
> matplotlib/mpldata/matplotlibrc')
> or with matplotlib.use()
>
> Any idea to fix it ?
>
> Thanks

Try:

import matplotlib
matplotlib.use('TkAgg')

before coding anything else

from the examples section of the matplotlib documentation
http://matplotlib.sourceforge.net/examples/user_interfaces/embedding_in_tk.html
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Re: os.popen output different from native shell output

[Thomas Guettler]

hi,

you get the popen output like this:

u...@unixhost> ls | cat


nickname schrieb:
> Hi all,
>I am a relative newbie to python, I am using os.popen to run an
> ls command. The output that I get using the read() function is
> different in look and feel from when I run the ls command natively
> from the shell (not via python). I display the ouput via python by
> using the print function on the variable that accepts the os.popen
> ().read() function.
...

 Thomas


-- 
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E-Mail: guettli (*) thomas-guettler + de
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Re: your favorite debugging tool?

[Michele Simionato]

On Aug 22, 4:25 pm, Esmail  wrote:
> Hi all,
>
> What is your favorite tool to help you debug your
> code?

The times when I would just use 'print' are long past. Nowadays I
spend lots of my time
with code written by others than myself. I use pdb all the time, and
now also ipdb
(ipdb is very cool if you are used to ipython).

  M.S.
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Re: print() and unicode strings (python 3.1)

[7stud]

On Aug 24, 10:09 pm, Ned Deily  wrote:
> In article
> ,
>
>
>
>  7stud  wrote:
> > On Aug 24, 2:41 pm, "Martin v. Löwis"  wrote:
> > > > I can't figure out a way to programatically set the encoding for
> > > > sys.stdout.  So where does that leave me?
>
> > > You should be setting the terminal encoding administratively, not
> > > programmatically.
>
> > The terminal encoding has always been utf-8.  It was not set
> > programmatically.
>
> > It seems to me that python 3.1's string handling is broken.
> > Apparently, in python 3.1 I am unable to explicitly set the encoding
> > of a string and print() it out with the result being human readable
> > text.  On the other hand, if I let python do the encoding implicitly,
> > python uses a codec I don't want it to.
>
> If you are running on a Unix-y system, check your locale settings (LANG,
> LC.*, et al).  I think you'll likely find that your locale is really not
> UTF-8.   The following was on Python 3.1 on OS X 10.5, similar results
> on Debian Linux:
>
> $ cat t3.py
> import sys
> print(sys.stdout.encoding)
> s = "¤"
> print(s.encode("utf-8"))
> print(s)
>
> $ export LANG=en_US.UTF-8
> $ python3.1 t3.py
> UTF-8
> b'\xe2\x82\xac'
> ¤
>
> $ export LANG=C
> $ python3.1 t3.py
> US-ASCII
> b'\xe2\x82\xac'
> Traceback (most recent call last):
>   File "t3.py", line 7, in 
> print(s)
> UnicodeEncodeError: 'ascii' codec can't encode character '\u20ac' in
> position 0: ordinal not in range(128)
>
> --
>  Ned Deily,
>  n...@acm.org

Hi,

Thanks for the response.  My OS is mac osx 10.4.11.  I'm not really
sure how to check my locale settings.  Here is some stuff I tried:

$ echo $LANG

$ echo $LC_ALL

$ echo $LC_CTYPE

$ locale
LANG=
LC_COLLATE="C"
LC_CTYPE="C"
LC_MESSAGES="C"
LC_MONETARY="C"
LC_NUMERIC="C"
LC_TIME="C"
LC_ALL="C"

$man locale
...
...
...

ENVIRONMENT:
LANG
Used as a substitute for any unset LC_* variable.  If LANG is unset it
will act as if set to "C".  If any of LANG or LC_* are set to invalide
values locale acts as if they are all unset.

===

As in your last example, my 'C' settings mean that an ascii codec is
used somewhere to encode() the unicode string.

--
The locale C or POSIX is a portable locale; its LC_CTYPE part
corresponds to the 7-bit ASCII character set.

http://linux.about.com/library/cmd/blcmdl3_setlocale.htm
--


Is this the way it works:


1) python sets the codec for sys.stdout to the LANG environment
variable.
2) It doesn't matter that my terminal's encoding is set to utf-8
because output has to pass through sys.stdout first.

So:

a) My terminal's environment is telling python(and all other programs
running in the terminal) that output sent to sys.stdout must be
encoded in ascii.
b) The solution is to set a LANG environment variable.


Why does echoing $LC_ALL or $LC_CTYPE just give me a blank string?


Previously, I've set environment variables that I want to be
permanent, e.g PATH, in ~/.bash_profile, so I did this:

~/.bash_profile:
--
...
...
LANG="en_US.UTF-8"
export LANG

and now python 3.1 acts like I expect it to:

---
import locale
import sys

print(locale.getlocale(locale.LC_CTYPE))
print(sys.stdout.encoding)


s = "€"
print(s)

print(s.encode("utf-8"))

--output:--
('en_US', 'UTF8')
UTF-8
€
b'\xe2\x82\xac'
--

In conclusion, as far as I can tell, if your python 3.1 program tries
to output a unicode string, and the unicode string cannot be encoded
by the codec specified in the user's LANG environment variable**, then
the user will get an encode error. Just because the programmer's
system can handle the output doesn't mean that another user's system
can.  I guess that's the way it goes: if a user's environment is
telling all programs that it only wants ascii output to go to the
screen(sys.stdout), you can't(or shouldn't) do anything about it.

**Or if the LANG environment variable is not present, then the codec
corresponding to the locale settings(C' corresponds to ascii).

some good locale info:
http://www.chemie.fu-berlin.de/chemnet/use/info/libc/libc_19.html
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unexpected token `;'

[bbarbero]

Hello to all!

I am struggling with a script in python for a while now, and decided  
to look for some help. I am running a code that takes commands from  
Marsyas(open source for Music analysis).


#!/Library/Frameworks/Python.framework/Versions/2.6/bin/python2.6
#!/bin/bashimport math
import re
import numpy
import string
import os.path
import sys
import commands



l =  
"/Users/bmorab/Audio_Projecto/Data/Palco/PP3_44_distance_matrix/PP3_44_5.mf"


Col = open(l, 'r')
colist= []
songlist = []
for line in Col:
#print line
song = os.path.split(line)[1]
#print song
songlist.append(song)
colist.append(line)



cmd = "sfplay " + colist[2]
print cmd
fileout = commands.getoutput(cmd)
print fileout



It basically reads song files from the .mf file, stores them in a list  
and play  one of the songs from the list. It does work with some music  
but mostly it gives an error like this:


sfplay  
/Volumes/HAL/Datasets/Audio/PalcoPrincipal/mp3_resampled_44100/10005.mp3


sh: -c: line 1: syntax error near unexpected token `;'
sh: -c: line 1: `; } 2>&1'


Ive been searching for the meaning of the error, and It really depends  
on the script, but I would conclude that I am missing a punctuation  
mark??


Thank you very much for taking your time reading my request.

Looking forward to hearing from you.

Regards,
Bea



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Re: unexpected token `;'

[mmelchert]

bbarb...@inescporto.pt wrote:

> Hello to all!
> 
> I am struggling with a script in python for a while now, and decided
> to look for some help. I am running a code that takes commands from
> Marsyas(open source for Music analysis).
> 
> #!/Library/Frameworks/Python.framework/Versions/2.6/bin/python2.6
> #!/bin/bashimport math  <<==
> import re
> import numpy

have a close look at the <<== line: I think you wanted it to read
import math rather than #!/bin/bashimport math?

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PyCon 2010 - Call for Tutorials

[Greg Lindstrom]

The period to submit proposals for PyCon 2010 in Atlanta, Georgia (USA) is
now open and will close on October 18.  Tutorials are 3-hour long classes on
a specific Python technique, package or technology and are taught by members
of the Python community.  If you have knowledge in a particular topic and
would like to be considered to teach a class we invite you to submit a
proposal outlining the material you would like to cover.  Once we receive
your proposal, we will "score" it based on content and then select 24
classes (subject to change) for presentation.

Class instructors will be paid $1000.00 per class.  If a class has more than
one teacher, the fee will be split between them.

Interested?  Click on over to the Tutorial Proposal
Pageto see more
details, examples of classes that have been requested in the
past (though you are free to submit a proposal on anything Python), an
example proposal and an empty template to help you prepare your own
proposal.  Once complete, email your proposal to
pycon-tutori...@python.orgso we can get it out to the evaluation
committee and get you on your way to
being a PyCon

Questions?  You can contact us at the PyCon Email
Listand we will get back with you.

We look forward to hearing from you!

Greg Lindstrom
Tutorial Coordinator
PyCon 2010 (Atlanta)
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Re: unexpected token `;'

[Diez B. Roggisch]

bbarb...@inescporto.pt wrote:

> Hello to all!
> 
> I am struggling with a script in python for a while now, and decided
> to look for some help. I am running a code that takes commands from
> Marsyas(open source for Music analysis).
> 
> #!/Library/Frameworks/Python.framework/Versions/2.6/bin/python2.6
> #!/bin/bashimport math

This is bogus. Replace it with

  #!/usr/bin/python

and put the "import math" on the next line.

Diez
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Re: Python for professsional Windows GUI apps?

[Wolfgang Keller]

> I need controls for business apps like access to databases, good data
> grid, printing reports (with or without barcodes), etc.

The area of _desktop_ database application development indeed looks like a vast 
and very hostile desert in the Python landscape.

The only framework that seems to be worth trying is Dabo. Unfortunately there's 
little documentation, and that's mostly outdated.

There's also Kiwi, but that's even less well documented.

And GNU Enterprise essentially seems to be dead.

Sincerely,

Wolfgang

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Re: can python make web applications?

[Mark]

On Sun, 23 Aug 2009 21:45:17 +0100, Goke Aruna wrote:

> A lot check this fantastic open source application,
> http://www.openerp.com, all done is python.

That does look impressive. Is that Django or Turbogears?


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Re: problem to write a THREAD enabled python extension

[Andreas Otto]

Stefan Behnel wrote:

> 
> You forgot to create a thread state for the new thread. See the
> PyThreadState_New() function.
> 

this does not really solve the problem even if the original error does no 
happen anymore ...

but a bucket of other error happen >>> sometimes <<< and this mean
that time and (I call it so) internal state stuff has influence on the 
problem and create errors like:

 1. http://mail.python.org/pipermail/python-list/2004-January/242740.html
 2. various PyThreadState_Get -> PyThreadState_Get: no current thread
 3. sometimes ThreadState has NULL sometimes not and NULL create an
 CORE for "tstate" pointer access operations
 4. ... a lot of other problems too

all problems together I come to the conclusion:

 1. I spend ~ 1week for a job done in C# or java in a day - and have no
 usable solution
 2. python need a couple of 100+ C API function for the same job
 java need 10+
 3. the design on the C-API is amateurish -> significant parts are
 implemented as GLOBAL variables
 4. the thread support is not more than a joke -> go to 3
 5. after pay a lot of effort to get something working the final solution 
 is significant slower than C# or JAVA
 6. you can not truss any-thing in python because you never know
 if under some circumstance you get a CORE 
 
the resulting PYTHON code is usable but not significant more readable
as JAVA, C* or even C++ code


mfg

  aotto1968

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Re: basic thread question

[Piet van Oostrum]

> sturlamolden  (s) wrote:

>s> On 25 Aug, 01:26, Piet van Oostrum  wrote:
>>> That's because it doesn't use copy-on-write. Thereby losing most of its
>>> advantages. I don't know SUA, but I have vaguely heard about it.

>s> SUA is a version of UNIX hidden inside Windows Vista and Windows 7
>s> (except in Home and Home Premium), but very few seem to know of it.
>s> SUA (Subsystem for Unix based Applications) is formerly known as
>s> Interix, which is a certified version of UNIX based on OpenBSD. If you
>s> go to http://www.interopsystems.com (a website run by Interop Systems
>s> Inc., a company owned by Microsoft), you will find a lot of common
>s> unix tools prebuilt for SUA, including Python 2.6.2.

>s> The NT-kernel supports copy-on-write fork with a special system call
>s> (ZwCreateProcess in ntdll.dll), which is what SUA's implementation of
>s> fork() uses.

I have heard about that also, but is there a Python implementation that
uses this? (Just curious, I am not using Windows.)
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Re: web frameworks that support Python 3

[Nobody]

On Sun, 23 Aug 2009 16:32:09 -0400, Albert Hopkins wrote:

> What's different about Python 3 is that there is only unicode strings,
> whereas Python 2 has a string type and a unicode type.

Python 2 has "str" (char) and "unicode" (wchar) types.

Python 3 has "bytes" (char) and "str" (wchar) types.

The main difference is that Python 3 uses unicode "by default", i.e.
string literals are unicode rather than byte strings, variables
such as sys.argv and os.environ contain unicode strings, etc.

There are other differences, e.g.:

+ Passing a "bytes" object where "str" is expected will raise an exception
rather than using an automatic conversion
+ Subscripting a "bytes" object returns an integer between 0 and 255
+ upper(), isalpha(), etc assume ASCII rather than the system encoding

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Re: unexpected token `;'

[Benjamin Kaplan]

On Tue, Aug 25, 2009 at 7:25 AM, Diez B. Roggisch wrote:

>
> > Hello to all!
> >
> > I am struggling with a script in python for a while now, and decided
> > to look for some help. I am running a code that takes commands from
> > Marsyas(open source for Music analysis).
> >
> > #!/Library/Frameworks/Python.framework/Versions/2.6/bin/python2.6
> > #!/bin/bashimport math
>
> This is bogus. Replace it with
>
>  #!/usr/bin/python
>
> and put the "import math" on the next line.
>


> Diez


It's not bogus. That is perfectly legitimate for using the user-installed
Python2.6 on OS X. /usr/bin/ is reserved for system programs on that
platform so it will always point to the system python install, which is
2.5.1 on Leopard and 2.3.5 on Tiger. That being said, the #!/bin/bash line
is what's screwing it up.
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Re: sgmllib.py

[Nobody]

On Mon, 24 Aug 2009 09:08:07 +0200, Stefan Behnel wrote:

> But note that sgmllib is a particularly cumbersome way to deal with HTML.

Mostly because it only provides a tokeniser, not a parser. Whoever wrote
it doesn't appear to understand the difference.

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Re: unexpected token `;'

[Peter Otten]

bbarb...@inescporto.pt wrote:

> I am struggling with a script in python for a while now, and decided
> to look for some help. I am running a code that takes commands from
> Marsyas(open source for Music analysis).

> cmd = "sfplay " + colist[2]
> print cmd
> fileout = commands.getoutput(cmd)

You have to ensure here that characters that have a special meaning for the 
shell are escaped correctly. The best approach is probably to use subprocess 
instead of commands:

fileoutput = subprocess.Popen(["sfplay", colist[2]],
stdout=subprocess.PIPE, 
stderr=subprocess.STDOUT).communicate()[0]  
  

Peter

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Re: your favorite debugging tool?

[Esmail]

Paul Rubin wrote:

Esmail  writes:

What is your favorite tool to help you debug your
code? I've been getting along with 'print' statements
but that is getting old and somewhat cumbersome.


Beyond print statements, I use pdb a lot.  Winpdb (www.winpdb.org) is
even better, but is kind of cumbersome to get working.


Hi,

2 quick questions.

Re pdb, if you have a 'pointer' (ie reference) to an object, is there
an easy way to dump out its contents, ie all of its members short of
writing a method that does that and then calling it?

Anyone know what is going on with the winpdb site? I haven't been able to
get to it in the last few days.

Thanks,
Esmail

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Re: your favorite debugging tool?

[Esmail]

Michele Simionato wrote:

On Aug 22, 4:25 pm, Esmail  wrote:

Hi all,

What is your favorite tool to help you debug your
code?


The times when I would just use 'print' are long past. Nowadays I
spend lots of my time
with code written by others than myself. I use pdb all the time, and
now also ipdb
(ipdb is very cool if you are used to ipython).


Never heard of ipdb, I'll have to check it out.

Thanks,
Esmail

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Re: your favorite debugging tool?

[Esmail]

Robert Marshall wrote:

On 24 Aug 2009, Paul Rubin wrote:


Esmail  writes:

What is your favorite tool to help you debug your
code? I've been getting along with 'print' statements
but that is getting old and somewhat cumbersome.

Beyond print statements, I use pdb a lot.  Winpdb (www.winpdb.org) is
even better, but is kind of cumbersome to get working.


And you can run it (pdb) within emacs - though I find a little roughness
in working out the exact interactions keeps ending up (ie the source
buffer displayed) in the wrong stack frame - afaict


Thanks Robert, I'll have to give that a try.

Esmail

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Re: [ANN] pyxser-1.2r --- Python-Object to XML serialization module

[Daniel Molina Wegener]

-BEGIN PGP SIGNED MESSAGE-
Hash: SHA512

Stefan Behnel 
on Tuesday 25 August 2009 01:23
wrote in comp.lang.python:


> Stefan Behnel wrote:
>> for all byte
>> strings, regardless of their encoding (since you can't even know if they
>> represent encoded text at all).
> 
> Hmm, having written that, I guess it's actually best to encode byte
> strings as base64 instead. Otherwise, null bytes and other special byte
> values won't pass.

  Sure, base64 is a good option for byte string input.

> 
> I also think that if the user wants readable output for text strings, it's
> reasonable to require Unicode input instead of byte strings. Handling text
> in byte strings is just too error prone.
> 
> Still, you may have to sanitize text input to make sure it doesn't contain
> special characters either. Take a look at the way lxml does it in the
> apihelpers.pxi source file, or read the XML spec on character content.

  Thanks, I will look for that. I must to do a better implementation on
handling byte strings, since would be many cases on where encoded strings
are mixed. For example different database inputs with different
encodings --- if those byte strings are not readed as Unicode strings.

  Both sanitizing and base64 encoding are good options, and also, both are
readable from other platforms. The problem with later implementations of
pyxser was that it was using *RawUnicodeEscape* which is not readable from
other platforms.

> 
> Stefan

Best regards,
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 ..O | dmw [at] coder [dot] cl | Open Standards
 OOO | http://coder.cl/| FOSS Developer
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Would there be work for a sysadmin who specializes in python?

[walterbyrd]

If I took the time to really learn to use python for sysadmin work,
would I be able to find jobs, or even contract jobs?

>From what I am seeing on the job boards etc., I would have to say no.
It looks to me as though I could possibly do that with perl, but not
python.

Of course, I could be missing something. Job board ads can be
deceptive.
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Re: Temat:, Re: IOError: [Errno 22] invalid mode ('wb') or filename: in windows xp while making tarfile

[ryniek]

On 25 Sie, 07:33, Dennis Lee Bieber  wrote:
> On Mon, 24 Aug 2009 14:23:41 -0700 (PDT), ryniek 
> declaimed the following in gmane.comp.python.general:
>
> > C:\Users\Ryniek's WinSe7en\Documents\My Dropbox\Aplikacje
> > \Moje_aplikacje\Pythonowe_aplikacje\Skrypty>python ba
> > ckuper.py -f E:\APLIKACJE\nowegg.exe E:\ MyGG
>
>         
>
> > OSError: [Errno 22] Invalid argument: 'E:\\MyGG(2009-08-24
> > 23:18:25).tar.bz2'
> > "
>
>         WHERE in your program are you creating that file name? Based upon
> the invocation line, all you are supplying is the E:\MyGG part...
> Somewhere you are creating a timestamp and attaching that to the prefix.
>
>         THAT is where you need to get rid of the colons -- the ones in the
> timestamp. Instead of 23:18:25 (or whatever the next run generates) you
> want something like 23_18_25...
> --
>         Wulfraed         Dennis Lee Bieber               KD6MOG
>         wlfr...@ix.netcom.com      HTTP://wlfraed.home.netcom.com/

Yep, i realized that it were THOSE colons. Thanks very much.
I think i must work on my perceptivity  : P

Thanks again.
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Re: print() and unicode strings (python 3.1)

[Nobody]

On Tue, 25 Aug 2009 03:41:54 -0700, 7stud wrote:

> Why does echoing $LC_ALL or $LC_CTYPE just give me a blank string?

Because the variables aren't set.

The default locale for a particular category (e.g. LC_CTYPE) is taken from
$LC_ALL if that is set, otherwise $LC_CTYPE, otherwise $LANG, otherwise
"C" is used.

Normally, you would either set LANG (and possibly some individual LC_*
variables), or LC_ALL. There's no point in setting all of them.

> In conclusion, as far as I can tell, if your python 3.1 program tries
> to output a unicode string, and the unicode string cannot be encoded
> by the codec specified in the user's LANG environment variable**, then
> the user will get an encode error. Just because the programmer's
> system can handle the output doesn't mean that another user's system
> can.  I guess that's the way it goes: if a user's environment is
> telling all programs that it only wants ascii output to go to the
> screen(sys.stdout), you can't(or shouldn't) do anything about it.
> 
> **Or if the LANG environment variable is not present, then the codec
> corresponding to the locale settings(C' corresponds to ascii).

The underlying OS primitive can only handle bytes. If you read or write a
(unicode) string, Python needs to know which encoding is used. For Python
file objects created by the user (via open() etc), you can specify the
encoding; for those created by the runtime (e.g. sys.stdin), Python uses
the locale's LC_CTYPE category to select an encoding.

Data written to or read from text streams is encoded or decoded using the
stream's encoding. Filenames are encoded and decoded using the
filesystem encoding (sys.getfilesystemencoding()). Anything else uses the
default encoding (sys.getdefaultencoding()).

In Python 3, text streams are handled using io.TextIOWrapper:

http://docs.python.org/3.1/library/io.html#text-i-o

This implements a stream which can read and/or write text data on top of
one which can read and/or write binary data. The sys.std{in,out,err}
streams are instances of TextIOWrapper. You can get the underlying
binary stream from the "buffer" attribute, e.g.:

sys.stdout.buffer.write(b'hello world\n')

If you need to force a specific encoding (e.g. if the user has specified
an encoding via a command-line option), you can detach the existing
wrapper and create a new one, e.g.:

sys.stdout = io.TextIOWrapper(sys.stdout.detach(), encoding = 
new_encoding)

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Re: Would there be work for a sysadmin who specializes in python?

[Esmail]

walterbyrd wrote:

If I took the time to really learn to use python for sysadmin work,
would I be able to find jobs, or even contract jobs?



FWIW, I think one of the qualities of a good system admin would be the ability
to work with a variety of tools and languages and not focus on one particular
language. Though Perl (not a favorite of mine at all :) seems to be quite
popular for admin type work, and of course knowing some sort of shell
programming etc would come in handy.

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Re: your favorite debugging tool?

[Ben Finney]

Esmail  writes:

> While I do believe in a minimalist approach (part of the reason I find
> Python so appealing), using print statements sometimes only goes so
> far (for me).

Right, which is where the Python interactive interpreter (which I failed
to mention in my initial response) comes in as my favourite debugging
tool.

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Re: your favorite debugging tool?

[Esmail]

Hi Ben,

Ben Finney wrote:


Whenever a simple output statement is too cumbersome for debugging, I
take it as a sign that the program is too cumbersome to follow.


I'll have to think about this .. though my gut says this is true :-)

re your other point about the interactive shell, I agree it's useful, but
to me still doesn't quite do what a full-fledged debugger can - but perhaps
that is a reflection of my skill with the shell at this point.

Always more to learn.

Esmail

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Re: proposal: add setresuid() system call to python

[Hrvoje Niksic]

travis+ml-pyt...@subspacefield.org writes:

> On Mon, Jul 20, 2009 at 04:10:35PM +0200, Hrvoje Niksic wrote:
>> To emulate the os-module-type calls, it's better to raise exceptions
>> than return negative values:
>> 
>> > def setresuid(ruid, euid, suid):
>> > return _setresuid(__uid_t(ruid), __uid_t(euid), __uid_t(suid))
>> 
>> def setresuid(ruid, euid, suid):
>> res = _setresuid(__uid_t(ruid), __uid_t(euid), __uid_t(suid))
>> if res < 0:
>> raise OSError('[Errno %d] %s' % (os.errno, errno.strerror(os.errno)))
>
> I am working on a module to implement all of this, but that raise command
> won't work in Python 2.6.1; it turns out that os.errno is a module, not
> an integer.  Does anyone know how to do what I want (that is, how to access
> the errno set in C functions)?

You should use ctypes.get_errno() instead of os.errno; sorry about that.

Also, when raising OSError, you should set the 'errno' attribute to the
appropriate code.
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Re: os.popen output different from native shell output

[Nobody]

On Tue, 25 Aug 2009 01:36:08 -0700, nickname wrote:

>I am a relative newbie to python, I am using os.popen to run an
> ls command. The output that I get using the read() function is
> different in look and feel from when I run the ls command natively
> from the shell (not via python).

As others have pointed out, the default behaviour of ls is different if
its output is a terminal.

> Is there an easy way to "mirror" the output. When python displays the
> output, how can it tell the bash shell that some of the entries are
> directories and they should appear blue on the bash shell, and that
> everything should not be appearing on 1 column only.

You can get the terminal-style behaviour even when using a pipe with:

ls -x --color

But why are you reading this information into Python then writing it
back out to the terminal?

If you're planning on processing the output within Python, both the
multi-column format and the escape sequences used for colour will make
such processing awkward.

If you want to enumerate the contents of a directory within Python, use
os.listdir().

If you want to generate coloured output, use the curses module, e.g.:

#!/usr/bin/env python

import sys
import curses

curses.setupterm()
setaf = curses.tigetstr('setaf') or ""
setab = curses.tigetstr('setab') or ""
origp = curses.tigetstr('op') or ""

def fg(c):
sys.stdout.write(curses.tparm(setaf, c))

def bg(c):
sys.stdout.write(curses.tparm(setab, c))

def orig():
sys.stdout.write(origp)

# example
bg(curses.COLOR_BLUE)
fg(curses.COLOR_YELLOW)
print "hello, world"
orig()

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Re: Protecting against callbacks queuing up?

[Esben von Buchwald]

Dennis Lee Bieber wrote:

On Mon, 24 Aug 2009 17:32:23 +0200, Esben von Buchwald
 declaimed the following in
gmane.comp.python.general:

I'm new to python, what is an after function and an after call? Couldn't 
find excact answer on google...? Do you have a link to some docs?


They would be particular to whatever GUI/event library is in use.
They aren't part of Python itself.


This is how the accelerometer is accessed
http://pys60.garage.maemo.org/doc/s60/node59.html

I found this called "after"...
http://pys60.garage.maemo.org/doc/s60/node12.html

would that be usable?

If so, how?
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Re: Items inheriting attributes from its container?

[Kreso]

Jan Kaliszewski  wrote:
[...]


Great! Thanks to all of you for advices and code.

K.
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Re: Would there be work for a sysadmin who specializes in python?

[Brent Bloxam]

walterbyrd wrote:

If I took the time to really learn to use python for sysadmin work,
would I be able to find jobs, or even contract jobs?


From what I am seeing on the job boards etc., I would have to say no.

It looks to me as though I could possibly do that with perl, but not
python.

Of course, I could be missing something. Job board ads can be
deceptive.


Being a system admin is about being able to handle to many different 
situations, and your tasks can often include automating various things 
and writing tools. Depending on the sort of place you're working in and 
the size of the IT department, you could find yourself doing a lot of 
work that lies outside of the standard job description for a system 
administrator. If you're looking to start out in the field, it would be 
better to have general knowledge, and as you gain experience you can 
begin to specialize.


Being adaptable is key, so specializing in python probably won't gain 
you any ground as a system administrator. That being said, knowing 
python will mean you have another tool in your chest, which is 
definitely a good thing. If there's one thing I'd recommend, if you're 
not going to focus on a windows environment, would be to at least get 
perl under your belt as well.

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Re: csv module and None values

[JKPeck]

On Aug 24, 10:43 pm, John Yeung  wrote:
> On Aug 24, 5:00 pm, Peter Otten <__pete...@web.de> wrote:
>
> > If I understand you correctly the csv.writer already does
> > what you want:
>
> > >>> w.writerow([1,None,2])
> > 1,,2
>
> > just sequential commas, but that is the special treatment.
> > Without it the None value would be converted to a string
> > and the line would look like this one:
>
> > 1,None,2
>
> No, I think he means he is getting
>
> >>> w.writerow([1,None,2])
>
> 1,"",2
>
> He evidently wants to quote "all" strings, but doesn't want None to be
> considered a string.
>
> John

Exactly so.  The requirement of the receiving program, which is out of
my control, is that all strings be quoted but a None in a numeric
field result in the ,, output rather than "".  Excel quotes strings
conditionally, which doesn't do what is needed in this case.  For
QUOTE_NONNUMERIC to quote None values makes some sense, but it gets in
the way of representing missing values in a numeric field.  It would
be nice to have a choice here in the dialects.

I thought of replacing the None values with float(nan), since that has
a numeric type, but unfortunately that results in writing the string
(unquoted) nan for the value.  So the sentinel approach seems to be
the best I can do.

Thanks,
Jon
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multiprocessing managers and socket connection.

[Chris]

I've been using multiprocessing managers and I really like the
functionality.

I have a question about reconnecting to a manager. I have a situation
where I start on one machine (A) a manager that is listening and then
on another machine (B) connects to that manager and uses its proxy
object to call functions on the manager's computer; this all works as
expected. But, if the manager from A shuts down, B's application won't
notice because in the MP code it ignores socket error
errno.ECONNREFUSED. If A becomes available again or is restarted, B
doesn't automatically reconnect either and continue its operation.
It's function is basically stopped.

Here is the code from connection.py:
while 1:
try:
s.connect(address)
except socket.error, e:
if e.args[0] != errno.ECONNREFUSED: # connection refused
debug('failed to connect to address %s', address)
raise
time.sleep(0.01)
else:
break

How can I have B automatically reconnect to A and continue its work
once A is available again?
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Re: Numeric literals in other than base 10 - was Annoying octal notation

[Steven D'Aprano]

On Mon, 24 Aug 2009 18:01:38 -0700, Mensanator wrote:

>> If you want your data file to have values entered in hex, or oct, or
>> even unary (1=one, 11=two, 111=three, =four...) you can.
> 
> Unary? I think you'll find that Standard Positional Number Systems are
> not defined for radix 1.

Of course not. But unary isn't a positional number system. It's a tally 
system, like my example above shows. Roman numerals are another tally 
system. Like Roman numerals, the disadvantages of unary are that you 
can't represent negative numbers, zero, or fractions, and anything but 
addition and subtraction is difficult. But if you want to use it, perhaps 
out of a sense of sadism towards your users, it's easy:

def int2unary(n):
return '1'*n

def unary2int(s):
n = 0
for c in s:
if c == '1': n+=1
else: raise ValueError('invalid unary string')
return n



-- 
Steven
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Re: your favorite debugging tool?

[Jean-Michel Pichavant]

Esmail wrote:

Hi Ben,

Ben Finney wrote:


Whenever a simple output statement is too cumbersome for debugging, I
take it as a sign that the program is too cumbersome to follow.


I'll have to think about this .. though my gut says this is true :-)

That is not always true. When it comes to implement complex tasks, you 
can't always avoid writing complex code. Python does not get your code 
more complex than your algorithm, but it cannot always simplify it.


Ben is right when he says that code can often be written in a more 
simpler manner, but they are some occasions when you have to write 
complex code, that the print debug statement won't be efficient enough 
to sort things out. I personally develop/maintain a full application 
written in python (and quite complex for some parts), using the ipdb 
debugger just saved my hours (days) of headache about some very 
difficult bug to spot

re your other point about the interactive shell, I agree it's useful, but
to me still doesn't quite do what a full-fledged debugger can - but 
perhaps

that is a reflection of my skill with the shell at this point.

Always more to learn.

Esmail



90% of the time, print statements + ipython shell will do the trick. The 
post mortem debugging is also very useful. Execute your  python file in 
ipython, then when it exits upon exception, execute

>>> import pdb ; pdb.pm()
You can then inspect the symbols easily.

JM
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TypeError: _getfullpathname() argument 1 must be (buffer overflow), not str in windows xp, while making tarfile

[Ryniek90]

Referring to my earlier posts:
http://groups.google.pl/group/comp.lang.python/browse_thread/thread/4e34f995800f5352?hl=pl

and

http://groups.google.pl/group/comp.lang.python/browse_thread/thread/abf5573b8fceb37e?hl=pl#

I've dealt with those errors. but now have another.
When my backup scripts starts to backup chosen file, python gave me 
Traceback:


"
C:\Users\Ryniek's WinSe7en\Documents\My 
Dropbox\Aplikacje\Moje_aplikacje\Pythonowe_aplikacje\Skrypty>python ba

ckuper.py -f F:\APLIKACJE\nowegg.exe F:\ MyGGBackup
Checking permissions for reading and writing...
Have permissions on [F:\APLIKACJE\nowegg.exe] for reading.
Have permissions on [F:\] for writing.
Preparing for backup [nowegg.exe]...
Starting backup...
Now adding [nowegg.exe]...
Traceback (most recent call last):
 File "backuper.py", line 197, in 
   main_meth()
 File "backuper.py", line 189, in main_meth
   paq.backup_file(pars.options.filename[0], pars.options.filename[1], 
pars.options.filename[2])

 File "backuper.py", line 127, in backup_file
   backup_obj.add(read_bin_obj)
 File "E:\WinSe7en Apps\APLIKACJE\ActiveState Python 
2.6\lib\tarfile.py", line 1948, in add

   if self.name is not None and os.path.abspath(name) == self.name:
 File "E:\WinSe7en Apps\APLIKACJE\ActiveState Python 
2.6\lib\ntpath.py", line 458, in abspath

   path = _getfullpathname(path)
TypeError: _getfullpathname() argument 1 must be (buffer overflow), not str
"

I've searched over google, but found only that is bug in Python ( 
http://bugs.python.org/issue4071  - in that issue bug is inside Python 
2.5.2 - i've got ActiveState Active Python with core Python 2.6.2), and 
another  info:   *http://tinyurl.com/lvyn7o  and **http://tinyurl.com/kn49vk

*

Here's my script code:
*http://paste.ubuntu.com/259310/

*Shouldn't that bug be patched already  :-?
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inconsistent sitecustomize.py importing...

[Chris Withers]

Hi All,

Give this sitecustomize.py:

print "ping"

...and this script:

#!/usr/local/bin/python2.5
print "pong!"

...both in ~/folder, I would expect the output from:

~$./folder/script

...to be:

ping
pong

...but sitecustomize.py is not imported :-(

If I do:

~$/usr/local/bin/python2.5 folder/script

...still no import.

However, if I do:

~/folder$/usr/local/bin/python2.5 script

...sitecustomize.py IS imported!

What gives?!

Chris

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   - http://www.simplistix.co.uk
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Re: csv module and None values

[Peter Otten]

JKPeck wrote:

> On Aug 24, 10:43 pm, John Yeung  wrote:
>> On Aug 24, 5:00 pm, Peter Otten <__pete...@web.de> wrote:
>>
>> > If I understand you correctly the csv.writer already does
>> > what you want:
>>
>> > >>> w.writerow([1,None,2])
>> > 1,,2
>>
>> > just sequential commas, but that is the special treatment.
>> > Without it the None value would be converted to a string
>> > and the line would look like this one:
>>
>> > 1,None,2
>>
>> No, I think he means he is getting
>>
>> >>> w.writerow([1,None,2])
>>
>> 1,"",2
>>
>> He evidently wants to quote "all" strings, but doesn't want None to be
>> considered a string.
>>
>> John
> 
> Exactly so.  The requirement of the receiving program, which is out of
> my control, is that all strings be quoted but a None in a numeric
> field result in the ,, output rather than "".  Excel quotes strings
> conditionally, which doesn't do what is needed in this case.  For
> QUOTE_NONNUMERIC to quote None values makes some sense, but it gets in
> the way of representing missing values in a numeric field.  It would
> be nice to have a choice here in the dialects.
> 
> I thought of replacing the None values with float(nan), since that has
> a numeric type, but unfortunately that results in writing the string
> (unquoted) nan for the value.  So the sentinel approach seems to be
> the best I can do.

How about:

>>> import csv, sys
>>> class N(int):
... def __str__(self): return ""
...
>>> pseudo_none = N()
>>> w = csv.writer(sys.stdout, quoting=csv.QUOTE_NONNUMERIC)
>>> w.writerow([1, "foo", pseudo_none, "bar"])
1,"foo",,"bar"

Peter

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Re: your favorite debugging tool?

[Ben Finney]

Esmail  writes:

> Hi Ben,
>
> Ben Finney wrote:
> >
> > Whenever a simple output statement is too cumbersome for debugging, I
> > take it as a sign that the program is too cumbersome to follow.
>
> I'll have to think about this .. though my gut says this is true :-)

Note that it's only a sign, *not* an ironclad guarantee. But it's the
right way to bet, IME.

> re your other point about the interactive shell, I agree it's useful,
> but to me still doesn't quite do what a full-fledged debugger can -
> but perhaps that is a reflection of my skill with the shell at this
> point.

This, on the other hand, I find even more consistent: if the code can't
be effectively inspected from the interactive interpreter, that's a sure
sign that its external interfaces are poor or its internal dependencies
too tightly coupled; or more likely both.

Fixing that set of problems is both useful for debugging *and* good
design.

-- 
 \ “Alternative explanations are always welcome in science, if |
  `\   they are better and explain more. Alternative explanations that |
_o__) explain nothing are not welcome.” —Victor J. Stenger, 2001-11-05 |
Ben Finney
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Even more inconsistent sitecustomize.py importing with PYTHONPATH rolled in...

[Chris Withers]

Chris Withers wrote:

However, if I do:

~/folder$/usr/local/bin/python2.5 script

...sitecustomize.py IS imported!


However, the following doesn't import sitecustomize.py:

~/folder$ ./script

While the following DOES import sitecustomize.py:

~/folder$ export PYTHONPATH=
~/folder$ ./script

Bizarrely, none of the following import sitecustomize.py:

~$ export PYTHONPATH=~/folder
~$ ./script

~$ export PYTHONPATH=~/folder/
~$ ./script

~$ export PYTHONPATH=~/folder
~/folder$ ./script

~$ export PYTHONPATH=~/folder/
~/folder$ ./script

Does anyone have any clue why there's such a huge level of inconsistency 
here?!


Chris

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   - http://www.simplistix.co.uk
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Re: Even more inconsistent sitecustomize.py importing with PYTHONPATH rolled in...

[Chris Withers]

Chris Withers wrote:

Bizarrely, none of the following import sitecustomize.py:

~$ export PYTHONPATH=~/folder
~$ ./script

~$ export PYTHONPATH=~/folder/
~$ ./script

~$ export PYTHONPATH=~/folder
~/folder$ ./script

~$ export PYTHONPATH=~/folder/
~/folder$ ./script


Okay, brain fail on my part, these do work, the others are still as 
described though...


Chris

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   - http://www.simplistix.co.uk
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Re: Putting together a larger matrix from smaller matrices

[Scott David Daniels]

Matjaz Bezovnik wrote:

If you are using numpy (which it sounds like you are):

IDLE 2.6.2
>>> import numpy as np
>>> v = np.array([[0,1,2],[3,4,5],[6,7,8]], dtype=float)
>>> v
array([[ 0.,  1.,  2.],
   [ 3.,  4.,  5.],
   [ 6.,  7.,  8.]])
>>> w = np.array([[10,11,12],[13,14,15],[16,17,18]], dtype=float)
>>> w
array([[ 10.,  11.,  12.],
   [ 13.,  14.,  15.],
   [ 16.,  17.,  18.]])
>>> r = np.zeros((6,6))
>>> r
array([[ 0.,  0.,  0.,  0.,  0.,  0.],
   [ 0.,  0.,  0.,  0.,  0.,  0.],
   [ 0.,  0.,  0.,  0.,  0.,  0.],
   [ 0.,  0.,  0.,  0.,  0.,  0.],
   [ 0.,  0.,  0.,  0.,  0.,  0.],
   [ 0.,  0.,  0.,  0.,  0.,  0.]])
>>> r[:3,:3] = v
>>> r
array([[ 0.,  1.,  2.,  0.,  0.,  0.],
   [ 3.,  4.,  5.,  0.,  0.,  0.],
   [ 6.,  7.,  8.,  0.,  0.,  0.],
   [ 0.,  0.,  0.,  0.,  0.,  0.],
   [ 0.,  0.,  0.,  0.,  0.,  0.],
   [ 0.,  0.,  0.,  0.,  0.,  0.]])
>>> r[3:,3:] = w
>>> r
array([[  0.,   1.,   2.,   0.,   0.,   0.],
   [  3.,   4.,   5.,   0.,   0.,   0.],
   [  6.,   7.,   8.,   0.,   0.,   0.],
   [  0.,   0.,   0.,  10.,  11.,  12.],
   [  0.,   0.,   0.,  13.,  14.,  15.],
   [  0.,   0.,   0.,  16.,  17.,  18.]])
>>>

In general, make the right-sized array of zeros, and at various points:
and you can ssign to subranges of the result array:

N = 3
result = np.zeros((len(parts) * N, len(parts) * N), dtype=float)
for n, chunk in enumerate(parts):
base = n * 3
result[base : base + 3, base : base + 3] = chunk

--Scott David Daniels
scott.dani...@acm.org
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Re: inconsistent sitecustomize.py importing...

[Steven D'Aprano]

On Tue, 25 Aug 2009 15:45:53 +0100, Chris Withers wrote:

> Hi All,
> 
> Give this sitecustomize.py:
[...]
> What gives?!

Perhaps this?

http://bugs.python.org/issue1734860


-- 
Steven
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Need help with Python scoping rules

[kj]

I have many years of programming experience, and a few languages,
under my belt, but still Python scoping rules remain mysterious to
me.  (In fact, Python's scoping behavior is the main reason I gave
up several earlier attempts to learn Python.)

Here's a toy example illustrating what I mean.  It's a simplification
of a real-life coding situation, in which I need to initialize a
"private" class variable by using a recursive helper function.

class Demo(object):
def fact(n):
if n < 2:
return 1
else:
return n * fact(n - 1)

_classvar = fact(5)

This code fails to compile, with the error "global name 'fact' not
defined".

Scanning the Python Language Reference page I see nothing that
would suggest to me a discussion of Python's scoping rules, let
alone anything that would help me solve the specific problem above.
I'm sure it's in there, *somewhere*, but it's anyone's guess where.

Likewise, my book, Beazley's "Python: Essential Reference" is of
no help.  I don't doubt that the answer to my question "is in there,
*somewhere*", but finding it (without reading the book sequentially
from page 1) is a tall order.

All that's left is trial-and-error, the worst kind of programming.
And still I can't find the right way to do this...  I've tried
every variant of this code that I can imagine, including decorating
fact with @staticmethod or @classmethod, etc., etc.  (In the latter
case, I get cryptic errors saying that the staticmethod or classmethod
object is not callable.  Or something like that.)

Needless to say, I'm pretty beat by this point.  Any help would be
appreciated.

Thanks,

kynn
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Re: Putting together a larger matrix from smaller matrices

[Matjaz Bezovnik]

On Tue, 25 Aug 2009 08:26:44 -0700, Scott David Daniels
 wrote:

>Matjaz Bezovnik wrote:
>
>If you are using numpy (which it sounds like you are):
>
>IDLE 2.6.2
> >>> import numpy as np
> >>> v = np.array([[0,1,2],[3,4,5],[6,7,8]], dtype=float)
> >>> v
>array([[ 0.,  1.,  2.],
>[ 3.,  4.,  5.],
>[ 6.,  7.,  8.]])
> >>> w = np.array([[10,11,12],[13,14,15],[16,17,18]], dtype=float)
> >>> w
>array([[ 10.,  11.,  12.],
>[ 13.,  14.,  15.],
>[ 16.,  17.,  18.]])
> >>> r = np.zeros((6,6))
> >>> r
>array([[ 0.,  0.,  0.,  0.,  0.,  0.],
>[ 0.,  0.,  0.,  0.,  0.,  0.],
>[ 0.,  0.,  0.,  0.,  0.,  0.],
>[ 0.,  0.,  0.,  0.,  0.,  0.],
>[ 0.,  0.,  0.,  0.,  0.,  0.],
>[ 0.,  0.,  0.,  0.,  0.,  0.]])
> >>> r[:3,:3] = v
> >>> r
>array([[ 0.,  1.,  2.,  0.,  0.,  0.],
>[ 3.,  4.,  5.,  0.,  0.,  0.],
>[ 6.,  7.,  8.,  0.,  0.,  0.],
>[ 0.,  0.,  0.,  0.,  0.,  0.],
>[ 0.,  0.,  0.,  0.,  0.,  0.],
>[ 0.,  0.,  0.,  0.,  0.,  0.]])
> >>> r[3:,3:] = w
> >>> r
>array([[  0.,   1.,   2.,   0.,   0.,   0.],
>[  3.,   4.,   5.,   0.,   0.,   0.],
>[  6.,   7.,   8.,   0.,   0.,   0.],
>[  0.,   0.,   0.,  10.,  11.,  12.],
>[  0.,   0.,   0.,  13.,  14.,  15.],
>[  0.,   0.,   0.,  16.,  17.,  18.]])
> >>>
>
>In general, make the right-sized array of zeros, and at various points:
>and you can ssign to subranges of the result array:
>
> N = 3
> result = np.zeros((len(parts) * N, len(parts) * N), dtype=float)
> for n, chunk in enumerate(parts):
> base = n * 3
> result[base : base + 3, base : base + 3] = chunk
>
>--Scott David Daniels
>scott.dani...@acm.org



Scott, thank you very much for the snippet.

It is exactly what I looked for; simple to read and obvious as to what
it does even a month later to a non-pythonist!

Matjaz
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Re: Graph library recommendations for large graphs

[Neal Becker]

VanL wrote:

> I am working on a project that will require building and querying large
> graph objects (initially 8M nodes, 30-40M edges; eventually 40M nodes,
> 100M edges). NetworkX seems to be the most popular, but I am concerned
> that a dict representation for nodes would use too much memory -- my
> initial tests suggest that a graph with 3M nodes and 12M edges creates
> substantial memory pressure on my machine.
> 
> Can anybody who has worked with large graphs before give a recommendation?
> 
> Thanks,
> 
> Van
> 
How about python-igraph?

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Re: TypeError: _getfullpathname() argument 1 must be (buffer overflow), not str in windows xp, while making tarfile

[MRAB]

Ryniek90 wrote:

Referring to my earlier posts:
http://groups.google.pl/group/comp.lang.python/browse_thread/thread/4e34f995800f5352?hl=pl 



and

http://groups.google.pl/group/comp.lang.python/browse_thread/thread/abf5573b8fceb37e?hl=pl# 



I've dealt with those errors. but now have another.
When my backup scripts starts to backup chosen file, python gave me 
Traceback:


"
C:\Users\Ryniek's WinSe7en\Documents\My 
Dropbox\Aplikacje\Moje_aplikacje\Pythonowe_aplikacje\Skrypty>python ba

ckuper.py -f F:\APLIKACJE\nowegg.exe F:\ MyGGBackup
Checking permissions for reading and writing...
Have permissions on [F:\APLIKACJE\nowegg.exe] for reading.
Have permissions on [F:\] for writing.
Preparing for backup [nowegg.exe]...
Starting backup...
Now adding [nowegg.exe]...
Traceback (most recent call last):
 File "backuper.py", line 197, in 
   main_meth()
 File "backuper.py", line 189, in main_meth
   paq.backup_file(pars.options.filename[0], pars.options.filename[1], 
pars.options.filename[2])

 File "backuper.py", line 127, in backup_file
   backup_obj.add(read_bin_obj)
 File "E:\WinSe7en Apps\APLIKACJE\ActiveState Python 
2.6\lib\tarfile.py", line 1948, in add

   if self.name is not None and os.path.abspath(name) == self.name:
 File "E:\WinSe7en Apps\APLIKACJE\ActiveState Python 2.6\lib\ntpath.py", 
line 458, in abspath

   path = _getfullpathname(path)
TypeError: _getfullpathname() argument 1 must be (buffer overflow), not str
"

I've searched over google, but found only that is bug in Python ( 
http://bugs.python.org/issue4071  - in that issue bug is inside Python 
2.5.2 - i've got ActiveState Active Python with core Python 2.6.2), and 
another  info:   *http://tinyurl.com/lvyn7o  and 
**http://tinyurl.com/kn49vk

*

Here's my script code:
*http://paste.ubuntu.com/259310/

*Shouldn't that bug be patched already  :-?

Are you giving it the contents of the file when it's actually expecting
the filename?
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Re: Protecting against callbacks queuing up?

[Hendrik van Rooyen]

On Tuesday 25 August 2009 15:21:16 Esben von Buchwald wrote:
> Dennis Lee Bieber wrote:
> > On Mon, 24 Aug 2009 17:32:23 +0200, Esben von Buchwald
> >  declaimed the following in
> >
> > gmane.comp.python.general:
> >> I'm new to python, what is an after function and an after call? Couldn't
> >> find excact answer on google...? Do you have a link to some docs?
> >
> > They would be particular to whatever GUI/event library is in use.
> > They aren't part of Python itself.
>
> This is how the accelerometer is accessed
> http://pys60.garage.maemo.org/doc/s60/node59.html
>
> I found this called "after"...
> http://pys60.garage.maemo.org/doc/s60/node12.html
>
> would that be usable?
Probably
>
> If so, how?

This is a guess, for your device,  but I suspect
something along these lines:

t = Ao_timer()

cb = t.after(100,thing_that_does_the_work(with_its_arguments))

Lots of assumptions here - the 100 should give you a tenth of a second...
Don't know what the arguments look like, and if you need to pass an instance 
(like self) - that would depend on where you are calling it from.

Play and see :-)

You should also be able to cancel the callback like this:

t.cancel(cb)

If you do it before the time out

- Hendrik

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Re: Code formatting question: conditional expression

[Nicola Larosa (tekNico)]

John Posner wrote:
> Is there any consensus on how to format a conditional expression
> that is too long for one line?

Here's my take:

excessblk = Block(total - P.BASE, srccol,
carry_button_suppress=True
) if total > P.BASE else None

--
Nicola Larosa - http://www.tekNico.net/

Nobody knows everything, and nobody is expected to be perfect
in the Ubuntu community (except of course the SABDFL).
 - https://launchpad.net/codeofconduct/1.0
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Re: Need help with Python scoping rules

[Martin P. Hellwig]

kj wrote:



Here's a toy example illustrating what I mean.  It's a simplification
of a real-life coding situation, in which I need to initialize a
"private" class variable by using a recursive helper function.


eh?



class Demo(object):
def fact(n):
if n < 2:
return 1
else:
return n * fact(n - 1)

_classvar = fact(5)



Sorry still doesn't make sense, I'll give it a try though:

class Demo(object):
"""Apparently a 'real-life coding situation'"""
def __init__(self):
# Look at http://docs.python.org/tutorial/classes.html
# for init explanation.
self.__class_var = self.fact(5)

def fact(self, number):
"""Look at http://docs.python.org/tutorial/classes.html why you 
need

self."""
if number < 2:
return(1)
else:
return_value = number * self.fact(number -1)
return(return_value)


TEST = Demo()
# Print the 'private' class variable
print(TEST._Demo__class_var)

--
MPH
http://blog.dcuktec.com
'If consumed, best digested with added seasoning to own preference.'
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Re: your favorite debugging tool?

[Falcolas]

On Aug 23, 1:21 am, Hendrik van Rooyen 
wrote:
> On Saturday 22 August 2009 16:49:22 Aahz wrote:
>
> > In article ,
>
> > Esmail   wrote:
> > >What is your favorite tool to help you debug your code? I've been
> > >getting along with 'print' statements but that is getting old and
> > >somewhat cumbersome.
>
> > Despite the fact that I've been using Python for more than a decade,
> > print is still my mainstay (or possibly logging to a file).
>
> Same here, although I have not been abusing python for as long as Aahz has
> been using it.
>
> ...
>
> And the final arbiter is of course the interactive prompt.
>
> - Hendrik

The only thing I would add to these comments is the fact that writing
helper functions for using print with complicated routines is very
simple, though perhaps not obvious. For example, consider the
following for unrolling list comprehensions or generators without
having to re-write them:

def trace(iterable):
for x in iterable:
print x
yield x

~G
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Re: Need help with Python scoping rules

[Diez B. Roggisch]

kj wrote:

> 
> 
> 
> I have many years of programming experience, and a few languages,
> under my belt, but still Python scoping rules remain mysterious to
> me.  (In fact, Python's scoping behavior is the main reason I gave
> up several earlier attempts to learn Python.)
> 
> Here's a toy example illustrating what I mean.  It's a simplification
> of a real-life coding situation, in which I need to initialize a
> "private" class variable by using a recursive helper function.
> 
> class Demo(object):
> def fact(n):
> if n < 2:
> return 1
> else:
> return n * fact(n - 1)
> 
> _classvar = fact(5)
> 
> This code fails to compile, with the error "global name 'fact' not
> defined".
> 
> Scanning the Python Language Reference page I see nothing that
> would suggest to me a discussion of Python's scoping rules, let
> alone anything that would help me solve the specific problem above.
> I'm sure it's in there, *somewhere*, but it's anyone's guess where.
> 
> Likewise, my book, Beazley's "Python: Essential Reference" is of
> no help.  I don't doubt that the answer to my question "is in there,
> *somewhere*", but finding it (without reading the book sequentially
> from page 1) is a tall order.
> 
> All that's left is trial-and-error, the worst kind of programming.
> And still I can't find the right way to do this...  I've tried
> every variant of this code that I can imagine, including decorating
> fact with @staticmethod or @classmethod, etc., etc.  (In the latter
> case, I get cryptic errors saying that the staticmethod or classmethod
> object is not callable.  Or something like that.)

Classes are not scopes. 

So the above doesn't work because name resolution inside functions/methods
looks for local variables first, then for the *global* scope. There is no
class-scope-lookup.

If you want anything else, you need to qualify it with a full name,
Demo.fact. Which isn't working for your example because "Demo" isn't
available yet.

But if you insist on the above methodology, you can do this:


class Demo(object):

def fact(n):
def inner(n):
if n < 2:
return 1
else:
return n * inner(n - 1)
return inner(n)

_classvar = fact(5)

This makes inner a *local* variable, which is found.

Diez

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Re: Web Services examples using "raw" xml?

[John Gordon]

In <4a936e84$0$31337$9b4e6...@newsspool4.arcor-online.net> Stefan Behnel 
 writes:

> > I tried WSDL.Proxy() from the SOAPpy package and eventually end up
> > with this error:
> > 
> > xml.parsers.expat.ExpatError: not well-formed (invalid token): line 1, 
> > column 6

> Is that while parsing the WSDL file? Have you tried pushing it through an
> XML parser yourself (or opening it with an XML editor) to see if it really
> is XML?

The 'invalid token' error happens if the argument to WSDL.Proxy() is a
string containing a URL beginning with https.  (It doesn't happen with a
http URL, but I'm stuck with https.)

As a next step, I grabbed the content from the https url in a browser,
saved it to a file, inserted it into the python code as a large string,
and passed that string to WSDL.Proxy().

That produced a KeyError 'targetNamespace' from this snippet of XML:

  http://www.w3.org/2001/XMLSchema";>
http://schemas.microsoft.com/exchange/services/2006/messages"; 
schemaLocation="messages.xsd"/>
  

I looked at the code and it apparently requires that the parent tag of
 have a targetNamespace attribute.  So I made one up and added
it, like so:

  http://www.w3.org/2001/XMLSchema"; targetNamespace="xyz">

I have no idea if this was the right thing to do, but it did let me advance
to the next error:

  Traceback (most recent call last):
  File "soappytest.py", line 1020, in ?
server = jrgWSDL.Proxy(wsdlFile)
  File "/home/gordonj/wsdl/jrgSOAPpy/jrgWSDL.py", line 75, in __init__
service = self.wsdl.services[0]
  File "/home/gordonj/wsdl/jrgwstools/Utility.py", line 631, in __getitem__
return self.list[key]
IndexError: list index out of range

After poking around in the code a bit more, I think that self.wsdl.services
is supposed to be a collection of all the services offered by the wsdl, but
it's actually empty, which is why it throws an error when it tries to
access the first element.

So that's where I'm stuck at the moment.  I have no idea why
self.wsdl.services isn't getting populated correctly -- or even if that's
the real problem!

Any suggestions?

-- 
John Gordon   A is for Amy, who fell down the stairs
gor...@panix.com  B is for Basil, assaulted by bears
-- Edward Gorey, "The Gashlycrumb Tinies"

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Re: Need help with Python scoping rules

[Jean-Michel Pichavant]

kj wrote:


I have many years of programming experience, and a few languages,
under my belt, but still Python scoping rules remain mysterious to
me.  (In fact, Python's scoping behavior is the main reason I gave
up several earlier attempts to learn Python.)

Here's a toy example illustrating what I mean.  It's a simplification
of a real-life coding situation, in which I need to initialize a
"private" class variable by using a recursive helper function.

class Demo(object):
def fact(n):
if n < 2:
return 1
else:
return n * fact(n - 1)

_classvar = fact(5)

This code fails to compile, with the error "global name 'fact' not
defined".
  

[snip]

fact is defined within the Demo class, so to access it, you'll need to 
prefix it with Demo:


_classvar = Demo.fact(5).

The problem is, Demo will raise a NameError exception.
The solution is pretty simple, cause your fact function seems to be 
unrelated to the Demo class :


def _fact(n):
   # some code

class Demo(object):
   _classvar = _fact(5)


It may happen that you *want* your fact within the Demo, in you example 
it's not that obvious, but I think Java would allow such following patern:


class Color:
   def __init__(self, r, g,b):
 pass
   BLACK = Color(0,0,0)

It make sens from a design point of view to put BLACK in the Color 
namespace. But I don't think it's possible with python.

You could trick the system using inheritance:

class Chrome:
   def __init__(self, r,g,b)
  pass
Putting all your code in the Chrome class then:

class Color(Chrome):
   BLACK = Chrome(0,0,0)

I'm not sure this is satisfying.

JM
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Re: Need help with Python scoping rules

[Jean-Michel Pichavant]

Diez B. Roggisch wrote
Classes are not scopes. 

  

Too bad, could have been handy.

JM
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Re: Need help with Python scoping rules

[Xavier Ho]

I'm not really quite sure what voodoo I did here, but my code seems to work
in Python 3.1.1 in the following way:

class Demo(object):
def func(self, n):
return n * 5
_f = func(None, 5)

d = Demo()
print(d._f)
print(d.func(5))

# OUTPUT
25
25

So, hmm?

Regards,

Ching-Yun "Xavier" Ho, Technical Artist

Contact Information
Mobile: (+61) 04 3335 4748
Skype ID: SpaXe85
Email: cont...@xavierho.com
Website: http://xavierho.com/
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Re: Need help with Python scoping rules

[Xavier Ho]

On Wed, Aug 26, 2009 at 2:14 AM, Diez B. Roggisch wrote:

>
> Classes are not scopes.
>
> So the above doesn't work because name resolution inside functions/methods
> looks for local variables first, then for the *global* scope. There is no
> class-scope-lookup.


Sorry, I'm coming here with sincere ignorance. If local variables and global
variables are not "scopes", then what would it be?

Cheers,
-Xav
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Re: Need help with Python scoping rules

[Diez B. Roggisch]

Jean-Michel Pichavant wrote:

> Diez B. Roggisch wrote
>> Classes are not scopes.
>>
>>   
> Too bad, could have been handy.

Nope. Because then a lot of people would write something like this:


class Foo(object):


   def bar(self):
   bar() # note the missing self.


And this would lead to errors because self was missing from the call
to "bar".

And you'd need a disambiguation for methodname/global-name-clashes. The
global-statement would work, but then code could break when all  of a
sudden a subclass defines a method that hitherto was only known as global.
So via subclassing, you introduce *arbitray* and hard to debug errors.

No. I'm certain, not a good idea.

Diez
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Re: conditional for-statement

[seb]

On Aug 23, 11:02 pm, Chris Rebert  wrote:
> On Sun, Aug 23, 2009 at 1:36 PM, seb wrote:
> > On Aug 23, 6:18 pm, John Posner  wrote:
> >> >> Hi,
>
> >> >> i was wondering if there is a syntax alike:
>
> >> >> for i in range(10) if i > 5:
> >> >>     print i
>
> >> > You can write
>
> >> > for i in filter(lambda i: i > 5, range(10)):
> >> >     print i
>
> >> > but
>
> >> > for i in range(10):
> >> >     if i > 5:
> >> >         print i
>
> >> > it' better readable, and
>
> >> > for i in range(6,10):
> >> >     print i
>
> >> > it's event better.
>
> >> How about using a generator expression instead of a list?
>
> >>   for i in (x for x in range(10) if x > 5):
> >>       print i
>
> >> -John
>
> > Indeed, but we could have the same syntax than for generators but
> > directly in the for statement as in
> > for variable in generator if condition:
> >    body
>
> > Is there a special reason for not doing so ? A rejected PEP ?
>
> It's not been added since it's completely unnecessary (see the several
> alternatives already presented by others).
> There have been a few other mailinglist threads on adding essentially
> the same syntax. None have proved fruitful.
>
> Cheers,
> Chris
> --http://blog.rebertia.com- Hide quoted text -
>
> - Show quoted text -

On Aug 23, 11:02 pm, Chris Rebert  wrote:
> On Sun, Aug 23, 2009 at 1:36 PM, seb wrote:
> > On Aug 23, 6:18 pm, John Posner  wrote:
> >> >> Hi,
>
> >> >> i was wondering if there is a syntax alike:
>
> >> >> for i in range(10) if i > 5:
> >> >> print i
>
> >> > You can write
>
> >> > for i in filter(lambda i: i > 5, range(10)):
> >> > print i
>
> >> > but
>
> >> > for i in range(10):
> >> > if i > 5:
> >> > print i
>
> >> > it' better readable, and
>
> >> > for i in range(6,10):
> >> > print i
>
> >> > it's event better.
>
> >> How about using a generator expression instead of a list?
>
> >>   for i in (x for x in range(10) if x > 5):
> >>   print i
>
> >> -John
>
> > Indeed, but we could have the same syntax than for generators but
> > directly in the for statement as in
> > for variable in generator if condition:
> >body
>
> > Is there a special reason for not doing so ? A rejected PEP ?
>
> It's not been added since it's completely unnecessary (see the several
> alternatives already presented by others).
> There have been a few other mailinglist threads on adding essentially
> the same syntax. None have proved fruitful.
>
> Cheers,
> Chris
> --http://blog.rebertia.com- Hide quoted text -
>
> - Show quoted text -

Tx Chris for your reply !

i am still a bit puzzle by the following.

I read in http://en.wikipedia.org/wiki/Python_syntax_and_semantics#Generators

"""Python 3.0 unifies all collection types by introducing dict and set
comprehensions, similar to list comprehensions:

>>> [ n*n for n in range(5) ] # regular list comprehension
[0, 1, 4, 9, 16]
>>>
>>> { n*n for n in range(5) } # set comprehension
{0, 1, 4, 16, 9}
>>>
>>> { n: n*n for n in range(5) } # dict comprehension
{0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
"""
and we can add to this list the quite similar syntax for generator
expressions.

On all these loop constructs, one can consistenly add filtering on a
condition by adding an "if ..." after the "for ... in ..." part (and
it looks to me difficult to argue, for instance, that we should not
allow filtering for dict comprehesion because we could get the same
result by some other construct)

If the "if ..." part after the "for ... in ..." is so much used in all
these list/dict/set comprehensions and in the generator expressions,
it makes sense to me to have it also for the "for as a statement"
syntax :
[ n*n for n in range(10) if n%3 == 0]
{ n*n for n in range(10) if n%3 == 0}
{ n: n*n for n in range(10) if n%3 == 0}
( n*n for n in range(10) if n%3 == 0)
for n in range(10) if n%3 == 0:
  print n*n

In fact, we often see the list comprehension [ n*n for n in range(10)
if n%3 == 0] explained as being equivalent to
l = []
for n in range(10):
  if n%3 == 0:
l.append(n)

We could as consistenly explain that the syntax

for n in range(10) if n%3==0:
  body

means

for n in range(10):
  if n%3==0:
body

This syntax has also the benefit of avoiding an extra level of
indentation (the one for the if) that bears no real meaning on a
structural level.

Maybe a PEP could do the job...

Sébastien
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Re: conditional for-statement

[seb]

On Aug 24, 12:05 am, Mel  wrote:
> seb wrote:
> > On Aug 23, 6:18 pm, John Posner  wrote:
> [ ... ]
> >> How about using a generator expression instead of a list?
>
> >> for i in (x for x in range(10) if x > 5):
> >> print i
>
> >> -John
>
> > Indeed, but we could have the same syntax than for generators but
> > directly in the for statement as in
> > for variable in generator if condition:
> >     body
>
> > Is there a special reason for not doing so ? A rejected PEP ?
>
> Well, the Zen of Python does say
>
> There should be one-- and preferably only one --obvious way to do it.
>
> Beyond that, I refer you to Gerald M. Weinberg's _The Psychology of Computer
> Programming_, specifically chapters 11 and 12, about Programming Languages,
> and their design.
>
> The proposal creates an case where one particular pair of syntactic
> constructs can be mooshed together.  OK for them, but everything else
> becomes an exception; what about
>
> while a==c if b != d:
>
> why not
>
> if b != d while a==c:
>

what would be the unambiguous meaning of any of these forms ?
they could be interesting but I do not understand them (yet!).


> or
>
> for a in range(7) if os.name == 'posix':
>
> It winds up burdening the programmers with remembering which constructs are
> and which are not mooshable.  Weinberg gave an example: FORTRAN had some
> stringent rules for what expressions were and were not allowed as array
> subscripts.  The result was that many programmers couldn't remember all the
> rules, and often avoided using legal forms, having forgotten they were
> legal.

indeed, the language features should stay as orthogonal as possible
(at least as a general rule)

>
> Maybe the line was already crossed when list comprehensions came into being,
> still, the damage is localized in a particular context: building a list.  It
> isn't out creating wild options in the program control flow at large.
>

indeed and it proved to be very useful & successful.
one cannot recommend to mix all features together as a general rule
but using common sense and practice, we can have some exceptions that
are definitely worth.

>         Mel.- Hide quoted text -
>
> - Show quoted text -

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Re: Web Services examples using "raw" xml?

[Stefan Behnel]

John Gordon wrote:
> Any suggestions?

Well, yes, see the link I posted.

http://effbot.org/zone/element-soap.htm

That might actually be the easiest way to get your stuff done, and it
avoids external dependencies (well, except for ElementTree, if you continue
to use Python <= 2.4).

Stefan
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Re: Need help with Python scoping rules

[John Posner]

Diez said:


Classes are not scopes. 


So the above doesn't work because name resolution inside functions/methods
looks for local variables first, then for the *global* scope. There is no
class-scope-lookup.


But http://docs.python.org/tutorial/classes.html says, in Section 9.3 "A 
First Look at Classes":


When a class definition is entered, a new namespace is created,
and used as the local scope — thus, all assignments to local variables
go into this new namespace. In particular, function definitions bind
the name of the new function here.


The following example confirms this:

class Spam(object):
clsvar_1 = 555
clsvar_2 = clsvar_1 + 222

def __init__(self):
print "Spam instance initialized"

sp = Spam()
print sp.clsvar_1, sp.clsvar_2

output:
Spam instance initialized
555 777


Does the OP (kj) have a legitimate gripe, though? I confess that I know 
nothing about Python's implementation -- I'm strictly a user. So it's 
just a suspicion of mine that
something special enables a recursive function definition to refer to 
the function's own name before the definition has been completed. It 
works at the module-namespace (i.e. global) level, and Diez's "toy 
example" shows that it works at function-namespace level:


   class Demo(object):

   def fact(n):
   def inner(n):
   if n < 2:
   return 1
   else:
   return n * inner(n - 1)
   return inner(n)

   _classvar = fact(5)


So why can't it work at the class-namespace level, too?

(BTW, Diez, your toy example is another demonstration that there *is* a 
class-scope-lookup: the "def" statement binds the name "fact" in the 
class scope, and the assignment statement looks up the name "fact" in 
that scope.)


-John

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Re: conditional for-statement

[Rami Chowdhury]

We could as consistenly explain that the syntax

for n in range(10) if n%3==0:
  body

means

for n in range(10):
  if n%3==0:
body

This syntax has also the benefit of avoiding an extra level of
indentation (the one for the if) that bears no real meaning on a
structural level.



I'm sorry, I don't see what you mean about avoiding the extra level of  
indentation? I can see a very real structural and logical distinction that  
the if-block makes, and IMO it's a good thing that that needs to be set  
apart.


On Tue, 25 Aug 2009 10:25:27 -0700, seb  wrote:



Tx Chris for your reply !

i am still a bit puzzle by the following.

I read in  
http://en.wikipedia.org/wiki/Python_syntax_and_semantics#Generators


"""Python 3.0 unifies all collection types by introducing dict and set
comprehensions, similar to list comprehensions:


[ n*n for n in range(5) ] # regular list comprehension

[0, 1, 4, 9, 16]


{ n*n for n in range(5) } # set comprehension

{0, 1, 4, 16, 9}


{ n: n*n for n in range(5) } # dict comprehension

{0: 0, 1: 1, 2: 4, 3: 9, 4: 16}
"""
and we can add to this list the quite similar syntax for generator
expressions.

On all these loop constructs, one can consistenly add filtering on a
condition by adding an "if ..." after the "for ... in ..." part (and
it looks to me difficult to argue, for instance, that we should not
allow filtering for dict comprehesion because we could get the same
result by some other construct)

If the "if ..." part after the "for ... in ..." is so much used in all
these list/dict/set comprehensions and in the generator expressions,
it makes sense to me to have it also for the "for as a statement"
syntax :
[ n*n for n in range(10) if n%3 == 0]
{ n*n for n in range(10) if n%3 == 0}
{ n: n*n for n in range(10) if n%3 == 0}
( n*n for n in range(10) if n%3 == 0)
for n in range(10) if n%3 == 0:
  print n*n

In fact, we often see the list comprehension [ n*n for n in range(10)
if n%3 == 0] explained as being equivalent to
l = []
for n in range(10):
  if n%3 == 0:
l.append(n)

We could as consistenly explain that the syntax

for n in range(10) if n%3==0:
  body

means

for n in range(10):
  if n%3==0:
body

This syntax has also the benefit of avoiding an extra level of
indentation (the one for the if) that bears no real meaning on a
structural level.

Maybe a PEP could do the job...

Sébastien




--
Rami Chowdhury
"Never attribute to malice that which can be attributed to stupidity" --  
Hanlon's Razor

408-597-7068 (US) / 07875-841-046 (UK) / 0189-245544 (BD)
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Re: basic thread question

[sturlamolden]

On 25 Aug, 13:33, Piet van Oostrum  wrote:

> I have heard about that also, but is there a Python implementation that
> uses this? (Just curious, I am not using Windows.)

On Windows we have three different versions of Python 2.6:

* Python 2.6 for Win32/64 (from python.org) does not have os.fork.

* Python 2.6 for Cygwin has os.fork, but it is non-COW and sluggish.

* Python 2.6 for SUA has a fast os.fork with copy-on-write.

You get Python 2.6.2 for SUA prebuilt by Microsoft from 
http://www.interopsystems.com.

Using Python 2.6 for SUA is not without surprices: For example, the
process is not executed from the Win32 subsystem, hence the Windows
API is inaccessible. That means we cannot use native Windows GUI.
Instead we must run an X11 server on the Windows subsystem (e.g. X-
Win32), and use the Xlib SUA has installed. You can compare SUA to a
stripped down Linux distro, on which you have to build and install
most of the software you want to use. I do not recommend using Python
for SUA instead of Python for Windows unless you absolutely need a
fast os.fork or have a program that otherwise requires Unix. But for
running Unix apps on Windows, SUA is clearly superior to Cygwin.
Licencing is also better: Programs compiled against Cygwin libraries
are GPL (unless you buy a commercial license). Program compiled
against SUA libraries are not.



Sturla Molden
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Re: Python for professsional Windows GUI apps?

[Gilles Ganault]

On Tue, 25 Aug 2009 13:24:39 +0200, Wolfgang Keller 
wrote:
>The area of _desktop_ database application development indeed looks like a 
>vast and very hostile desert in the Python landscape.
>
>The only framework that seems to be worth trying is Dabo. Unfortunately 
>there's little documentation, and that's mostly outdated.
>
>There's also Kiwi, but that's even less well documented.
>
>And GNU Enterprise essentially seems to be dead.

Combined with the comment above about issues with printing, it looks
like Python for GUI apps isn't a very good idea :-/

I'd be interested in checking out commercial applications written in
Python for the Windows OS, if there are any.

Thank you.
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Re: Need help with Python scoping rules

[7stud]

On Aug 25, 12:11 pm, John Posner  wrote:
> Diez said:
>
>
>
> > Classes are not scopes.
>
> > So the above doesn't work because name resolution inside functions/methods
> > looks for local variables first, then for the *global* scope. There is no
> > class-scope-lookup.
>
> Buthttp://docs.python.org/tutorial/classes.htmlsays, in Section 9.3 "A
> First Look at Classes":
>
> When a class definition is entered, a new namespace is created,
> and used as the local scope — thus, all assignments to local variables
> go into this new namespace. In particular, function definitions bind
> the name of the new function here.
>
> The following example confirms this:
>
> class Spam(object):
> clsvar_1 = 555
> clsvar_2 = clsvar_1 + 222
>
> def __init__(self):
> print "Spam instance initialized"
>
> sp = Spam()
> print sp.clsvar_1, sp.clsvar_2
>
> output:
> Spam instance initialized
> 555 777
>
> Does the OP (kj) have a legitimate gripe, though? I confess that I know


I guess a counter example would be something like this:

y = "hello"

class Demo(object):
y = "goodbye"

def __init__(self):
self.x = 10
print y

Demo()

--output:--
hello


>
> nothing about Python's implementation -- I'm strictly a user. So it's
> just a suspicion of mine that
> something special enables a recursive function definition to refer to
> the function's own name before the definition has been completed.
>

python ignores the names inside a function when it creates the
function.  This "program" will not produce an error:


def f():
print x

python parses the file and creates the function object and assigns the
function object to the variable f.  It's not until you execute the
function that python will raise an error.  The same thing happens with
the recursive function.


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Re: Python for professsional Windows GUI apps?

[David Boddie]

On Tuesday 25 August 2009 13:24, Wolfgang Keller wrote:

> The area of _desktop_ database application development indeed looks like a
> vast and very hostile desert in the Python landscape.
> 
> The only framework that seems to be worth trying is Dabo. Unfortunately
> there's little documentation, and that's mostly outdated.
> 
> There's also Kiwi, but that's even less well documented.
> 
> And GNU Enterprise essentially seems to be dead.

There's also Camelot, if that's the kind of thing you're after:

  http://www.conceptive.be/projects/camelot

David
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Re: Putting together a larger matrix from smaller matrices

[sturlamolden]

On 25 Aug, 17:37, Matjaz Bezovnik  wrote:

> Scott, thank you very much for the snippet.
>
> It is exactly what I looked for; simple to read and obvious as to what
> it does even a month later to a non-pythonist!


Since you were talking about matrices, observe that numpy has a matrix
subclass of ndarray, which e.g. changes the meaning of the * operator
mean indicate matrix multiplication. Thus,

>>> import numpy as np
>>> np.eye(4)
array([[ 1.,  0.,  0.,  0.],
   [ 0.,  1.,  0.,  0.],
   [ 0.,  0.,  1.,  0.],
   [ 0.,  0.,  0.,  1.]])
>>> np.matrix(np.eye(4))
matrix([[ 1.,  0.,  0.,  0.],
[ 0.,  1.,  0.,  0.],
[ 0.,  0.,  1.,  0.],
[ 0.,  0.,  0.,  1.]])

>>> a = np.ones((4,4))
>>> a*a
array([[ 1.,  1.,  1.,  1.],
   [ 1.,  1.,  1.,  1.],
   [ 1.,  1.,  1.,  1.],
   [ 1.,  1.,  1.,  1.]])
>>> b = np.matrix(a)
>>> b*b
matrix([[ 4.,  4.,  4.,  4.],
[ 4.,  4.,  4.,  4.],
[ 4.,  4.,  4.,  4.],
[ 4.,  4.,  4.,  4.]])
>>> b**2
matrix([[ 4.,  4.,  4.,  4.],
[ 4.,  4.,  4.,  4.],
[ 4.,  4.,  4.,  4.],
[ 4.,  4.,  4.,  4.]])
>>> b**4
matrix([[ 64.,  64.,  64.,  64.],
[ 64.,  64.,  64.,  64.],
[ 64.,  64.,  64.,  64.],
[ 64.,  64.,  64.,  64.]])

In Matlab, you use .* vs. * and .^ vs. ^ to obtain the same effect. In
NumPy we use different classes for arrays and matrices.



Sturla Molden



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Re: Putting together a larger matrix from smaller matrices

[Robert Kern]

On 2009-08-24 21:30 PM, Matjaz Bezovnik wrote:

Dear all,

I'm but a layman so do not take offence at this maybe over simple
question.

This is something which is done often in FEM methods, and the alike.

I have matrix A of 3x3 elements, and B, of the same number of
elements, 3x3.

What would be the most obvious way to assemble a matrix which:
a11 a12 a13
a21 a22 a23
a31 a32 a33+b11 b12 b13
   b21 b22 b23
   b31 b32 b33

(the missing elements = zero)

(you see the pattern - if there was a third matrix C, it would
"connect" to b33 on the main diagonal)


You will certainly want to use numpy for this and ask questions on the numpy 
mailing list.


  http://www.scipy.org/Mailing_Lists

I believe that someone recently posted a recipe for constructing such "block 
diagonal" arrays. I think it will be included in a future release of numpy.


--
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
 that is made terrible by our own mad attempt to interpret it as though it had
 an underlying truth."
  -- Umberto Eco

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Re: os.popen output different from native shell output

[nickname]

On Aug 25, 6:16 am, Nobody  wrote:
> On Tue, 25 Aug 2009 01:36:08 -0700, nickname wrote:
> >        I am a relative newbie to python, I am using os.popen to run an
> > ls command. The output that I get using the read() function is
> > different in look and feel from when I run the ls command natively
> > from the shell (not via python).
>
> As others have pointed out, the default behaviour of ls is different if
> its output is a terminal.
>
> > Is there an easy way to "mirror" the output. When python displays the
> > output, how can it tell the bash shell that some of the entries are
> > directories and they should appear blue on the bash shell, and that
> > everything should not be appearing on 1 column only.
>
> You can get the terminal-style behaviour even when using a pipe with:
>
>         ls -x --color
>
> But why are you reading this information into Python then writing it
> back out to the terminal?
>
> If you're planning on processing the output within Python, both the
> multi-column format and the escape sequences used for colour will make
> such processing awkward.
>
> If you want to enumerate the contents of a directory within Python, use
> os.listdir().
>
> If you want to generate coloured output, use the curses module, e.g.:
>
> #!/usr/bin/env python
>
> import sys
> import curses
>
> curses.setupterm()
> setaf = curses.tigetstr('setaf') or ""
> setab = curses.tigetstr('setab') or ""
> origp = curses.tigetstr('op') or ""
>
> def fg(c):
>     sys.stdout.write(curses.tparm(setaf, c))
>
> def bg(c):
>     sys.stdout.write(curses.tparm(setab, c))
>
> def orig():
>     sys.stdout.write(origp)
>
> # example
> bg(curses.COLOR_BLUE)
> fg(curses.COLOR_YELLOW)
> print "hello, world"
> orig()

wow guys! thanks for all the great leads! this is awesome!

The reason why I want to do this is because I am going to do a little
project. I will write a python script called ls which will log the
time and username and then will show the actual ls output. I want this
to be transparent and so want to throw the ls output (via python)
exactly as it will be in native shell execution.

I know there's history files I can look up, but I just am exploring my
own intermediate-logging-layer the functionality for which is executed
right before the actual command is executed.

Thanks,
-A
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Re: Python for professsional Windows GUI apps?

[sturlamolden]

On 25 Aug, 20:30, Gilles Ganault  wrote:

> Combined with the comment above about issues with printing, it looks
> like Python for GUI apps isn't a very good idea :-/

With pywin32, printing is the same as for any other Windows app (you
get MFC for Python).

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Re: Numeric literals in other than base 10 - was Annoying octal notation

[Mensanator]

On Aug 25, 9:14 am, Steven D'Aprano  wrote:
> On Mon, 24 Aug 2009 18:01:38 -0700, Mensanator wrote:
> >> If you want your data file to have values entered in hex, or oct, or
> >> even unary (1=one, 11=two, 111=three, =four...) you can.
>
> > Unary? I think you'll find that Standard Positional Number Systems are
> > not defined for radix 1.
>
> Of course not. But unary isn't a positional number system. It's a tally
> system, like my example above shows. Roman numerals are another tally
> system. Like Roman numerals, the disadvantages of unary are that you
> can't represent negative numbers, zero, or fractions, and anything but
> addition and subtraction is difficult. But if you want to use it, perhaps
> out of a sense of sadism towards your users, it's easy:
>
> def int2unary(n):
>     return '1'*n
>
> def unary2int(s):
>     n = 0
>     for c in s:
>         if c == '1': n+=1
>         else: raise ValueError('invalid unary string')
>     return n

But without insignificant leading 0's, I fail to see the relevance
of unary to this discussion. And what would you call a tally system
of radix 2? Certainly not binary.

>
> --
> Steven

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Re: your favorite debugging tool?

[Robert Kern]

On 2009-08-25 09:49 AM, Ben Finney wrote:

Esmail  writes:


Hi Ben,

Ben Finney wrote:


Whenever a simple output statement is too cumbersome for debugging, I
take it as a sign that the program is too cumbersome to follow.


I'll have to think about this .. though my gut says this is true :-)


Note that it's only a sign, *not* an ironclad guarantee. But it's the
right way to bet, IME.


re your other point about the interactive shell, I agree it's useful,
but to me still doesn't quite do what a full-fledged debugger can -
but perhaps that is a reflection of my skill with the shell at this
point.


This, on the other hand, I find even more consistent: if the code can't
be effectively inspected from the interactive interpreter, that's a sure
sign that its external interfaces are poor or its internal dependencies
too tightly coupled; or more likely both.


And a debugger is a great tool to help you figure out exactly why your code 
doesn't actually have the wonderful decoupling that you thought you designed 
into it so you can fix it. :-)


--
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
 that is made terrible by our own mad attempt to interpret it as though it had
 an underlying truth."
  -- Umberto Eco

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Re: Python for professsional Windows GUI apps?

[sturlamolden]

On 25 Aug, 13:24, Wolfgang Keller  wrote:

> The area of _desktop_ database application development indeed looks like a 
> vast and very hostile desert in the Python landscape.

Yes, you don't have drag-and-drop database tools like MS Access or
FoxPro. You actually have to use a database API (such as pyodbc or
pymssql) with GUI (tkinter, wxPython, PyGTK, PyQt, MFC) manually. If
you need a framework for this, you should not be developing software
anyway.

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Re: proposal: add setresuid() system call to python

[travis]

On Tue, Aug 25, 2009 at 03:03:12PM +0200, Hrvoje Niksic wrote:
> You should use ctypes.get_errno() instead of os.errno; sorry about that.
> 
> Also, when raising OSError, you should set the 'errno' attribute to the
> appropriate code.

How does that compare to:

raise pythonapi.PyErr_SetFromErrno(py_object(OSError))

?
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Re: Waiting for a subprocess to exit

[Aahz]

In article ,
Miles Kaufmann   wrote:
>
>debacle[1]).  Leaving shell=3DFalse makes scripts more secure and =20
>robust; besides, when I'm putting together a command and its =20
>arguments, it's as convenient to build a list (['mycmd', 'myarg']) as =20=
>
>it is a string (if not more so).

unless you want to use "~" on Mac or Unix.
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Re: Simple IRC library

[jason]

On 2009-08-24 01:39:21 -0600, devaru  said:


Hi all,
I am new to Python language. I want to capture(either in database or a
file) the conversation in IRC.


Fed.


Please suggest me some simple IRC library or code snippet for this.


I have used the oyoyo library with success. It's pretty nice and has a 
framework for bots which you might be interested in looking at.


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

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Re: Need help with Python scoping rules

[John Posner]

7stud said:

python ignores the names inside a function when it creates the
function.  This "program" will not produce an error:


def f():
print x

python parses the file and creates the function object and assigns the
function object to the variable f.  It's not until you execute the
function that python will raise an error.  The same thing happens with
the recursive function.
  



Thanks for that explanation. So in the OP's example:

Class Demo(object):
   def fact(n):
   if n < 2:
   return 1
   else:
   return n * fact(n - 1)

   _classvar = fact(5)


... no failure occurs when "fact(5)" is invoked, because the lookup of 
"fact" in the local scope is a class-scope-lookup, which succeeds. The 
failure occurs on the first recursive invocation of fact() in the 
statement "return n * fact(n - 1)": the function-scope-lookup of "fact" 
fails, and then the interpreter falls back to a global-scope-lookup of 
"fact", which also fails.


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Re: Object Reference question

[Aahz]

In article ,
Hendrik van Rooyen   wrote:
>On Friday 21 August 2009 08:07:18 josef wrote:
>>
>> My main focus of this post is: "How do I find and use object reference
>> memory locations?"
>
 a = [1,2,3,4]
 id(a)
>8347088
  

Of course, that doesn't actually allow you to do anything...
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Context manager to temporarily change the variable of a register [aka write swap(a,b)]

[Evan Driscoll]

(If you don't want to read the following, note that you can answer my
question by writing a swap function.)

I want to make a context manager that will temporarily change the
value of a variable within the scope of a 'with' that uses it. This is
inspired by a C++ RAII object I've used in a few projects. Ideally,
what I want is something like the following:

x = 5
print x   # prints 5
with changed_value(x, 10):
print x  # prints 10
print x  # prints 5

This is similar to PEP 343's example 5 ("Redirect stdout temporarily";
see http://www.python.org/dev/peps/pep-0343/), except that the
variable that I want to temporarily change isn't hard-coded in the
stdout_redirected function.

What I want to write is something like this:
@contextmanager
def changed_value(variable, temp_value):
old_value = variable
variable = temp_value
try:
yield None
finally:
variable = old_value
with maybe a check in 'finally' to make sure that the value hasn't
changed during the execution of the 'with'.

Of course this doesn't work since it only changes the binding of
'variable', not whatever was passed in, and I kind of doubt I can
stick a "&" and "*" in a couple places to make it do what I want. :-)

So my question is: is what I want possible to do in Python? How?

I think it might be possible to rig something up by passing in the
variable that i want to change as a *string* and looking up that
string in a dictionary somewhere, but I think what I need is the locals
() dictionary of the calling function, and I'm not sure how to get
that.

Thanks,
Evan Driscoll
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Re: your favorite debugging tool?

[Robert Kern]

On 2009-08-25 06:57 AM, Esmail wrote:

Michele Simionato wrote:

On Aug 22, 4:25 pm, Esmail  wrote:

Hi all,

What is your favorite tool to help you debug your
code?


The times when I would just use 'print' are long past. Nowadays I
spend lots of my time
with code written by others than myself. I use pdb all the time, and
now also ipdb
(ipdb is very cool if you are used to ipython).


Never heard of ipdb, I'll have to check it out.


It's not really a separate thing, just the pdb integration into the IPython 
interactive shell (which I highly recommend that you check out).


--
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless enigma
 that is made terrible by our own mad attempt to interpret it as though it had
 an underlying truth."
  -- Umberto Eco

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Re: os.popen output different from native shell output

[Thomas Guettler]

In one of the first chapters of "Advanced programming in the unix
environment (second edition)" there is explained how a unix shell works.

You could write you own shell using python. This way the python
interpreter gets stared only once, and not for every call to "ls".



Have fun,
  Thomas

nickname schrieb:
> wow guys! thanks for all the great leads! this is awesome!
> 
> The reason why I want to do this is because I am going to do a little
> project. I will write a python script called ls which will log the
> time and username and then will show the actual ls output. I want this
> to be transparent and so want to throw the ls output (via python)
> exactly as it will be in native shell execution.
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Re: conditional for-statement

[Falcolas]

On Aug 25, 11:25 am, seb  wrote:
> We could as consistenly explain that the syntax
>
> for n in range(10) if n%3==0:
>   body
>
> means
>
> for n in range(10):
>   if n%3==0:
>     body
>
> This syntax has also the benefit of avoiding an extra level of
> indentation (the one for the if) that bears no real meaning on a
> structural level.
>
> Maybe a PEP could do the job...
>
> Sébastien

So, what part of the statement does the "if" statement belong to;
particularly a concern considering this is valid python:

for x in y if y else z:
body

You can always do the following at the cost of 6 symbols, and the gain
of clarity:

for n in (x for x in y if y%3==0):
body

~G
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Python, qt, and lgpl

[Terry Reedy]

"
New LGPL Python bindings for Qt slither into the light

A new set of LGPL-licensed Python bindings for Qt has been announced. 
The project, which is backed by Nokia, will make it easier for 
commercial software developers to adopt Python and Qt for rapid 
application development."


http://arstechnica.com/open-source/news/2009/08/openbossa-announces-new-lgpl-python-bindings-for-qt.ars

Will be good news if realized.

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Re: Context manager to temporarily change the variable of a register [aka write swap(a,b)]

[Emile van Sebille]

On 8/25/2009 12:33 PM Evan Driscoll said...


So my question is: is what I want possible to do in Python? 


Probably not with immutables (as in your example) -- maybe otherwise.

Emile

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break unichr instead of fix ord?

[rurpy]

In Python 2.5 on Windows I could do [*1]:

  # Create a unicode character outside of the BMP.
  >>> a = u'\U00010040'

  # On Windows it is represented as a surogate pair.
  >>> len(a)
  2
  >>> a[0],a[1]
  (u'\ud800', u'\udc40')

  # Create the same character with the unichr() function.
  >>> a = unichr (65600)
  >>> a[0],a[1]
  (u'\ud800', u'\udc40')

  # Although the unichr() function works fine, its
  # inverse, ord(), doesn't.
  >>> ord (a)
  TypeError: ord() expected a character, but string of length 2 found

On Python 2.6, unichr() was "fixed" (using the word
loosely) so that it too now fails with characters outside
the BMP.

  >>> a = unichr (65600)
  ValueError: unichr() arg not in range(0x1) (narrow Python build)

Why was this done rather than changing ord() to accept a
surrogate pair?

Does not this effectively make unichr() and ord() useless
on Windows for all but a subset of unicode characters?
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Re: conditional for-statement

[seb]

On Aug 25, 9:42 pm, Falcolas  wrote:
> On Aug 25, 11:25 am, seb  wrote:
>
>
>
> > We could as consistenly explain that the syntax
>
> > for n in range(10) if n%3==0:
> >   body
>
> > means
>
> > for n in range(10):
> >   if n%3==0:
> >     body
>
> > This syntax has also the benefit of avoiding an extra level of
> > indentation (the one for the if) that bears no real meaning on a
> > structural level.
>
> > Maybe a PEP could do the job...
>
> > Sébastien

>
> So, what part of the statement does the "if" statement belong to;
> particularly a concern considering this is valid python:
>
> for x in y if y else z:
>     body
>
can this be done in list/set/dict comprehensions/generator
expressions ?

> You can always do the following at the cost of 6 symbols, and the gain
> of clarity:
>
> for n in (x for x in y if y%3==0):
>     body

it is in fact precisely to avoid this sort of line:
  for n in (x for x in y if x%3==0):
and have instead the (more readable IMO) line
  for n in y if n%3==0:
with:
 - 1 "for ... in ..." instead of 2 (where one is the repetition of the
other)
 - no parentheses
 - no extra technical variable with local binding to the expression
generator ('x')
it looks more pythonic to me but it is a personal taste.

>
> ~G

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Re: Context manager to temporarily change the variable of a register [aka write swap(a,b)]

[Evan Driscoll]

On Aug 25, 2:33 pm, Evan Driscoll  wrote:
> I want to make a context manager that will temporarily change the
> value of a variable within the scope of a 'with' that uses it. This is
> inspired by a C++ RAII object I've used in a few projects. Ideally,
> what I want is something like the following:

Okay, so I think I actually got this with some consultation with a
friend. Critiques?

from contextlib import contextmanager
import inspect

def get_parents_var(offset, var):
f = inspect.stack()[offset][0]
if var in f.f_locals:
return f.f_locals[var]
else:
return f.f_globals[var]

def set_parents_var(offset, var, val):
f = inspect.stack()[offset][0]
if var in f.f_locals:
f.f_locals[var] = val
elif var in f_globals:
f.f_globals[var] = val
else:
assert False


@contextmanager
def changed_value_tb(var_name, temp_value):
# 1 is here, 2 will be the implicit next() function, 3 is the
real caller
offset = 3
old_value = get_parents_var(offset, var_name)
set_parents_var(offset, var_name, temp_value)
try:
yield None
finally:
set_parents_var(offset, var_name, old_value)


x = 5
print x   # prints 5
with changed_value_tb("x", 10):
print x  # prints 10
print x  # prints 5
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Re: Need help with Python scoping rules

[Diez B. Roggisch]

John Posner schrieb:

Diez said:


Classes are not scopes.
So the above doesn't work because name resolution inside 
functions/methods

looks for local variables first, then for the *global* scope. There is no
class-scope-lookup.


But http://docs.python.org/tutorial/classes.html says, in Section 9.3 "A 
First Look at Classes":


When a class definition is entered, a new namespace is created,
and used as the local scope — thus, all assignments to local variables
go into this new namespace. In particular, function definitions bind
the name of the new function here.


The following example confirms this:

class Spam(object):
clsvar_1 = 555
clsvar_2 = clsvar_1 + 222

def __init__(self):
print "Spam instance initialized"

sp = Spam()
print sp.clsvar_1, sp.clsvar_2

output:
Spam instance initialized
555 777


Does the OP (kj) have a legitimate gripe, though? I confess that I know 
nothing about Python's implementation -- I'm strictly a user. So it's 
just a suspicion of mine that
something special enables a recursive function definition to refer to 
the function's own name before the definition has been completed. It 
works at the module-namespace (i.e. global) level, and Diez's "toy 
example" shows that it works at function-namespace level:


   class Demo(object):

   def fact(n):
   def inner(n):
   if n < 2:
   return 1
   else:
   return n * inner(n - 1)
   return inner(n)

   _classvar = fact(5)


So why can't it work at the class-namespace level, too?


See my other post on what name lookup with class-scope *inside* 
functions would mean.


Diez
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Re: Context manager to temporarily change the variable of a register [aka write swap(a,b)]

[Evan Driscoll]

On Aug 25, 3:07 pm, Evan Driscoll  wrote:
> Okay, so I think I actually got this with some consultation with a
> friend. Critiques?

This is wrong; it's not quite working right. It does with the example
I posted, but not in a more thorough test.

I'm still ignoring the "you can't do this" answers for a little while
more and continuing to try to hack on it. :-)

Evan
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