Re: Problem with keyboard up/down arrows in Python 2.4 interpreter

[Benjamin Kaplan]

On Fri, Mar 25, 2011 at 2:25 AM, Julien  wrote:
> On Mar 22, 5:37 pm, Benjamin Kaplan  wrote:
>> On Tue, Mar 22, 2011 at 2:27 AM, Julien  wrote:
>> > Hi,
>>
>> > I'm having problems when typing the up/down arrows in the Python 2.4
>> > interpreter (exact version: Python 2.4.6 (#1, Mar  3 2011, 15:45:53)
>> > [GCC 4.2.1 (Apple Inc. build 5664)] on darwin).
>>
>> > When I press the up arrow it outputs "^[[A" and when I press the down
>> > arrow it outputs "^[[B".
>>
>> > I've google it and it looks like it might be an issue with the
>> > readline not being installed or configured properly. Is that correct?
>> > If so, how can I fix this issue?
>>
>> > Many thanks.
>>
>> > Kind regards,
>>
>> > Julien
>> > --
>>
>> How did you install Python? If you used Macports, it looks like
>> readline support is a separate port for 2.4. Try installing
>> py-readline.
>>
>>
>>
>>
>>
>>
>>
>> >http://mail.python.org/mailman/listinfo/python-list
>
> Hi,
>
> Which readline package should I install? I've tried with 'pip install
> py-readline' but that package doesn't seem to exist. I've tried with
> 'pyreadline' (without the dash) but that didn't fix the issue.
>
> Many thanks,
>
> Julien

As I stated above, py-readline is for if you're using Macports, which
is a package manager for Mac OS X.  If you installed Python through
some other means, I'm not sure why you don't have readline installed
already, because it should be built with the rest of the Python
modules.


> http://mail.python.org/mailman/listinfo/python-list
>
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Re: functools.partial doesn't work without using named parameter

[Benjamin Kaplan]

On Fri, Mar 25, 2011 at 2:30 AM, Paddy  wrote:
> Hi, I just found the following oddity where for function fsf1 I am forced to 
> use a named parameter for correct evaluation and was wondering why it doesn't 
> work, yet the example from the docs of wrapping int to create basetwo doesn't 
> need this?
> The example:
>
 from functools import partial
 basetwo = partial(int, base=2)
 basetwo('10010')
> 18

 def fs(f, s): return [f(value) for value in s]
>
 def f1(value): return value * 2
>
 s = [0, 1, 2, 3]
 fs(f1, s)
> [0, 2, 4, 6]

 fsf1 = partial(fs, f=f1)
 fsf1(s)
> Traceback (most recent call last):
>  File "", line 1, in 
>    fsf1(s)
> TypeError: fs() got multiple values for keyword argument 'f'
 # BUT
 fsf1(s=s)
> [0, 2, 4, 6]

>
> Would someone help?
>

If you hand partial a keyword argument, it treats it as a keyword
argument. If you want to hand it a positional argument, hand it a
positional argument.

>>> fsf1 = partial(fs,f1)
>>> fsf1(s)
[0, 2, 4, 6]
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Re: functools.partial doesn't work without using named parameter

[Ian Kelly]

On Fri, Mar 25, 2011 at 12:30 AM, Paddy  wrote:
 def fs(f, s): return [f(value) for value in s]

Note that your "fs" is basically equivalent to the "map" builtin,
minus some of the features.

 fsf1 = partial(fs, f=f1)
 fsf1(s)
> Traceback (most recent call last):
>  File "", line 1, in 
>    fsf1(s)
> TypeError: fs() got multiple values for keyword argument 'f'
 # BUT
 fsf1(s=s)
> [0, 2, 4, 6]

>
> Would someone help?

When you invoke a partial application, it just adds the positional
arguments passed to partial to the positional arguments passed in, and
it adds the keyword arguments passed to partial to the keyword
arguments passed in.  Using partial to specify f as a keyword argument
does not change the fact that it is also the first positional
argument.  So the call `partial(fs, f=f1)(s)` is equivalent to `fs(s,
f=f1)`.  In the latter case, 's' is being passed positionally as the
first argument (i.e. 'f') and 'f1' is being passed by keyword as the
'f' argument, resulting in 'f' being passed in twice.  The partial
application is equivalent, so it does the same thing.

The call `partial(fs, f=f1)(s=s)`, however, is equivalent to `fs(f=f1,
s=s)`, which is fine.

Moral of the story: if you pass in an argument by keyword, then the
following arguments must be passed by keyword as well (or not at all),
regardless of whether you're using partial or not.
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Re: functools.partial doesn't work without using named parameter

[Steven D'Aprano]

On Thu, 24 Mar 2011 23:30:29 -0700, Paddy wrote:

> Hi, I just found the following oddity where for function fsf1 I am
> forced to use a named parameter for correct evaluation and was wondering
> why it doesn't work, yet the example from the docs of wrapping int to
> create basetwo doesn't need this? The example:
> 
 from functools import partial
 basetwo = partial(int, base=2)
 basetwo('10010')
> 18

When you call basetwo, it gets passed one positional argument and one 
keyword argument. The positional arguments are bound from left to right, 
as is normal in Python:

int expects to be called like int(a, [base=]b)
int gets passed two arguments: int('10010', base=2)

so all is well. The string '10010' gets bound to the first argument, and 
the keyword argument 2 gets bound to the second.



 def fs(f, s): return [f(value) for value in s]
> 
 def f1(value): return value * 2
> 
 s = [0, 1, 2, 3]
 fs(f1, s)
> [0, 2, 4, 6]

All these f's and s's give me a headache. It's easier to discuss if you 
give them distinctive names: spam, ham, eggs are conventions in Python, 
foo, bar, baz in some other languages.



 fsf1 = partial(fs, f=f1)
 fsf1(s)
> Traceback (most recent call last):
>   File "", line 1, in 
> fsf1(s)
> TypeError: fs() got multiple values for keyword argument 'f'


fs expects to be called like fs(f, s). It gets called with one positional 
argument, [0,1,2,3], which gets bound to the left-most parameter f, and 
one keyword argument, f1, which *also* gets bound to the parameter f 
(only by name this time, instead of by position).


 # BUT
 fsf1(s=s)
> [0, 2, 4, 6]

Now, because you're calling fsf1 with keyword argument, fs gets called:

fs(f=f1, s=[0,1,2,3])



-- 
Steven
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Re: functools.partial doesn't work without using named parameter

[Ian Kelly]

On Fri, Mar 25, 2011 at 1:03 AM, Ian Kelly  wrote:
> Moral of the story: if you pass in an argument by keyword, then the
> following arguments must be passed by keyword as well (or not at all),
> regardless of whether you're using partial or not.

To be clear, you can also just pass f1 into partial positionally, like so:

>>> fsf1 = partial(fs, f1)
>>> fsf1(s)
[0, 2, 4, 6]
>>> fsf1(s=s)
[0, 2, 4, 6]
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Re: functools.partial doesn't work without using named parameter

[Paddy]

Thanks Ian, Benjamin, and Steven.

I now know why it works as it does.

Thinking about it a little more, Is it reasonable to *expect* partial acts as 
it does, rather than this way being an implementation convenience? (That was 
written as a straight question not in any way as a dig).

I had thought that partial had enough information to, and would in fact, remove 
named parameter f from the signature of fsf1 returning something that could be 
called that is the equivalent of:

def fsf1_( s ): ...

I accept that that is not done, but would welcome discussion on if my 
expectation above was reasonable. 

Thanks guys :-)
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Re: functools.partial doesn't work without using named parameter

[Paddy]

Aha!

Thanks Ian for this new snippet. It is what I will use for my current example. 
(But please see my third posting on this too).
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Re: Problem with keyboard up/down arrows in Python 2.4 interpreter

[Ned Deily]

In article 
,
 Benjamin Kaplan  wrote:
> As I stated above, py-readline is for if you're using Macports, which
> is a package manager for Mac OS X.

... in which case you probably want:

   sudo port install py-readline

> If you installed Python through
> some other means, I'm not sure why you don't have readline installed
> already, because it should be built with the rest of the Python
> modules.

For releases prior to Python 2.6 and Python 3.2, to build the Python 
readline module, you need to have installed a local version of the GNU 
readline library, a library which is not included in Mac OS X.  Starting 
with Python 2.6 and with a deployment target of Mac OS X 10.5 or higher, 
the Python readline module will be automatically linked with the 
Apple-supplied BSD editline (libedit) library.

P.S to Julien: Python 2.4 is *really* old now and is no longer supported 
by the Python developers.  It probably won't build correctly on current 
OS X 10.6 without some help.  Python 2.7.1 and Python 3.2 are the 
current releases.

-- 
 Ned Deily,
 n...@acm.org

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Re: why memoizing is faster

[Andrea Crotti]

Terry Reedy  writes:
>
> For the reason Stefan explained and hinted above. Try the following instead:
>
> def fib_iter(n, _cache = [1,1]):
>   k = len(_cache)
>   if n >= k:
> for i in range(k, n+1):
>_cache.append(_cache[i-2] + _cache[i-1])
>   return _cache[n]
>
> This should be slightly faster than the crazy-key cache for the
> memoized recursive version.
>

You're right this is much faster, also of the recursive function, so it
was just my iterative version that was bad...

But I don't see what's the difference, I don't get what's the difference
between that and:

def fib_iter(n):
ls = [0, 1]
for i in range(2, n+1):
ls.append(ls[i-2] + ls[i-1])

return ls[n]


Your version runs in 
250 ns, while this version runs in 25.1 us.
How can passing a default "_cache" argument can make such a difference?

What I find interesting in all this is that the memoize function works
also because python has the mutable types "problem" as argument of
functions, which every beginner stumbles upon at some point.

If it had a more "expected" behaviour of instantiating a new cache
dictionary every time this trick would not be possible.
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Re: why memoizing is faster

[Stefan Behnel]

Andrea Crotti, 25.03.2011 09:49:

Terry Reedy writes:


For the reason Stefan explained and hinted above. Try the following instead:

def fib_iter(n, _cache = [1,1]):
   k = len(_cache)
   if n>= k:
 for i in range(k, n+1):
_cache.append(_cache[i-2] + _cache[i-1])
   return _cache[n]

This should be slightly faster than the crazy-key cache for the
memoized recursive version.



You're right this is much faster, also of the recursive function, so it
was just my iterative version that was bad...

But I don't see what's the difference, I don't get what's the difference
between that and:

def fib_iter(n):
 ls = [0, 1]
 for i in range(2, n+1):
 ls.append(ls[i-2] + ls[i-1])

 return ls[n]


Your version runs in
250 ns, while this version runs in 25.1 us.
How can passing a default "_cache" argument can make such a difference?


Terry's version is playing with the fact that default arguments are only 
instantiated once, i.e. (unless overridden by passing an explicit argument) 
the "_cache" is shared over all calls to the function. This is similar to 
what your memoization decorator does, but without the additional dict. And, 
it also "suffers" from the same timing problem that I mentioned before.


Stefan

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Re: Guido rethinking removal of cmp from sort method

[Antoon Pardon]

On Thu, Mar 24, 2011 at 11:49:53PM +, Steven D'Aprano wrote:
> On Thu, 24 Mar 2011 17:47:05 +0100, Antoon Pardon wrote:
> 
> > However since that seems to be a problem for you I will be more
> > detailed. The original poster didn't ask for cases in which cmp was
> > necessary, he asked for cases in which not using cmp was cumbersome.
> 
> I'm the original poster, and that's not what I said. I said:
> 
> "If anyone has any use-cases for sorting with a comparison function that 
> either can't be written using a key function, or that perform really 
> badly when done so, this would be a good time to speak up."
> 
> You'll notice that I said nothing about whether writing the code was easy 
> or cumbersome, and nothing about readability.

Well fine. I should have realised the question was just a pretense and that
there really never was any intention to consider the reactions, because
the answer is already fixed. Of course a key function can always be written,
it may just need a specific class to implement the specific order. Likewise
there is no reason to expect the order-functions to preform worse when
implemented in a class, rather than in a function.

-- 
Antoon Pardon
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Re: dynamic assigments

[scattered]

On Mar 24, 11:08 pm, Tim Leslie  wrote:
> On 25 March 2011 13:51, scattered  wrote:
>
> > Here is another possibility: you are using Python *interactively* in
> > solving cryptograms (as a matter of fact - I was doing exactly this
> > yesterday in trying to solve some Playfair ciphers). You have a
> > ciphertext that is a stream of letters in the range A...Z. You need to
> > consult frequencies of letters, pairs of letters, triples of letters,
> > and quadruples of letters that occur. So, you write a script that
> > steps through the cipher text, creates a dictionary which records
> > frequencies of strings of length <= 4, and, as an added convienence,
> > creates bindings of frequencies to these strings. Thus - if you want
> > to know how often, say, EFW occurs in the ciphertext you just type EFW
> > (rather than freq["EFW"])
>
> And what happens when you want to know the frequency of "if", "def",
> "for" or any other variable which matches a keyword?
>
> Tim

>>> IF = 3
>>> if IF > 1: print("No problem")
>>> 'No problem'

In a *program* such things are silly - for interactive use where you
have motivation to have a family of pre-defined bindings available for
possible use, it is perfectly ok. If Python *did* have an upper-case
keyword (does it? I couldn't think of any), e.g. NULL, then of course
you could write your script to check for that, and for those special
cases (which are unlikely to occur as substrings of a cipher text) you
could make the binding to something like fNULL instead.
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Re: dynamic assigments

[scattered]

On Mar 25, 1:44 am, Steven D'Aprano  wrote:
>
> In my earlier post, I described the dynamic creation of variables as:
>
> "... something you should *nearly* always avoid doing." [Emphasis added.]
>
> Congratulations, you've found one of the few exceptions. Of course an
> interactive shell must allow you to create variables interactively. It
> would hardly be interactive if you couldn't. This is why interactive
> shells are often called a REPL: Read Eval (or Exec) Print Loop.
>
> Note also that I was describing *variables*. Although there are a lot of
> similarities between variables and instance attributes (so much so that
> some other languages call them both variables), there are some subtle
> differences, and those differences are important. Dynamic *attribute*
> creation is not anywhere near as bad a code-smell as dynamic variables:
>
> setattr(instance, name, value)  # A slight whiff, but usually okay.
>
> globals()[name] = value  # Smells pretty bad, but very occasionally okay.
>
> exec(name + " = " + str(value))  # Reeks like Satan's armpit after a long
> # day mucking out the pits of excrement with the souls of the Damned.
>

I realize that I'm in a distinct minority of Python users, but I tend
to write scripts which consist of nothing but function definitions
intended to be invoked at a REPL. In effect, I used Python as a sort
of highly-programmable calculator. When I saw the OP, it struck me as
something having obvious utility for the sorts of things that I, in
fact, use Python for. I defer to your judgement that such dynamic
bindings are a bad idea in any production code.

> > solving cryptograms (as a matter of fact - I was doing exactly this
> > yesterday in trying to solve some Playfair ciphers).
>
> If you're interested in ciphers, you might find this useful:
>
> http://pypi.python.org/pypi/obfuscate
>

Thanks for the tip

>  You have a
>
> > ciphertext that is a stream of letters in the range A...Z. You need to
> > consult frequencies of letters, pairs of letters, triples of letters,
> > and quadruples of letters that occur. So, you write a script that steps
> > through the cipher text, creates a dictionary which records frequencies
> > of strings of length <= 4, and, as an added convienence, creates
> > bindings of frequencies to these strings.
>
> I don't call that a convenience. I call that a problem. What happens when
> your cipher text includes
>
> "...aBzNk6YPq7psGNQ1Pj?lenprem1zGWdefmspzzQ..."
>
> How many problems can you see there?
>

I specified that the cipher text consists of characters in the range A
to Z (note the case). There is a common convention that, when solving
traditional text-based ciphers, you write the ciphertext in upper case
and the (unkown) plain text in lower case. That way you are dealing
with tentative partial decryptions you can keep track of which letters
in your partial solution are drawn from the original ciphertext and
which are from your guesses

> > Thus - if you want to know how
> > often, say, EFW occurs in the ciphertext you just type EFW (rather than
> > freq["EFW"]) and the Python shell returns the frequency.
>
> Sounds like a terrible idea. What do you do when you want to know how
> often "len" or "1xy" or "???" or "def" occurs?
>
> --
> Steven- Hide quoted text -
>
> - Show quoted text -

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Re: why memoizing is faster

[Tim Wintle]

On Fri, 2011-03-25 at 09:49 +0100, Andrea Crotti wrote:
> Terry Reedy  writes:
> >
> > For the reason Stefan explained and hinted above. Try the following instead:
> >
> > def fib_iter(n, _cache = [1,1]):
> >   k = len(_cache)
> >   if n >= k:
> > for i in range(k, n+1):
> >_cache.append(_cache[i-2] + _cache[i-1])
> >   return _cache[n]
> >
> I don't get what's the difference between that and:
> 
> def fib_iter(n):
> ls = [0, 1]
> for i in range(2, n+1):
> ls.append(ls[i-2] + ls[i-1])
> 
> return ls[n]

> How can passing a default "_cache" argument can make such a difference?

Default values are initialised at definition time.

Since lists are mutable, the _cache variable really is a cache - the
following time you call the function it will store all the previous
calculations.

e.g.

>>> def default_value(_cache=[]):
...   _cache.append(len(_cache))
...   print _cache
... 
>>> default_value()
[0]
>>> default_value()
[0, 1]
>>> default_value()
[0, 1, 2]
>>> default_value()
[0, 1, 2, 3]



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Re: why memoizing is faster

[eryksun ()]

On Thursday, March 24, 2011 8:12:22 PM UTC-4, Terry Reedy wrote:
>
> If Python did what some have asked, which is to make 'recursive' 
> functions actually recursive by replacing a local variable that matches 
> the function name (in this 'fib') with a direct reference to the 
> function itself, as a constant (and this could be done), then the 
> wrapper would not get called from within the function.

Regarding this I have question about function attributes. Is there an 
equivalent of 'self' for functions? I've seen people use function attributes as 
local static variables, but this seems problematic when all you have is a 
global reference to the function. The original reference might get deleted. 
Then when your function tries to reference its 'static' variable you'll get a 
NameError exception. For example:

In [1]: def test1(n):
   ...: test1.a = n

In [2]: test1(10); test1.a
Out[2]: 10

In [3]: test2 = test1; test2.a
Out[3]: 10

In [4]: del test1

In [5]: test2(20); test2.a
---
NameError


Should such a function always take a reference to itself as the first 
parameter?  

In [6]: def test1(f, n):
   ...: f.a = n

In [7]: test1(test1, 10); test1.a
Out[7]: 10

In [8]: test2 = test1; test2.a
Out[8]: 10

In [9]: del test1

In [10]: test2(test2, 20); test2.a
Out[10]: 20

Granted, this would be better handled in a class.
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Re: Guido rethinking removal of cmp from sort method

[Stefan Behnel]

Antoon Pardon, 25.03.2011 10:21:

On Thu, Mar 24, 2011 at 11:49:53PM +, Steven D'Aprano wrote:

On Thu, 24 Mar 2011 17:47:05 +0100, Antoon Pardon wrote:


However since that seems to be a problem for you I will be more
detailed. The original poster didn't ask for cases in which cmp was
necessary, he asked for cases in which not using cmp was cumbersome.


I'm the original poster, and that's not what I said. I said:

"If anyone has any use-cases for sorting with a comparison function that
either can't be written using a key function, or that perform really
badly when done so, this would be a good time to speak up."

You'll notice that I said nothing about whether writing the code was easy
or cumbersome, and nothing about readability.


Well fine. I should have realised the question was just a pretense and that
there really never was any intention to consider the reactions, because
the answer is already fixed.


I don't think it is. It's just not as simple as "see, I have an artificial 
use case here, so you *must* put the feature back in the language".


Stefan

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Re: why memoizing is faster

[Andrea Crotti]

"eryksun ()"  writes:

>
> Regarding this I have question about function attributes. Is there an
> equivalent of 'self' for functions? I've seen people use function
> attributes as local static variables, but this seems problematic when
> all you have is a global reference to the function. The original
> reference might get deleted. Then when your function tries to
> reference its 'static' variable you'll get a NameError exception. For
> example:
>
> In [1]: def test1(n):
>...: test1.a = n
>
> In [2]: test1(10); test1.a
> Out[2]: 10
>
> In [3]: test2 = test1; test2.a
> Out[3]: 10
>

[...]

I had never seen such a thing, but why would this make sense at all?
When does it make sense logically for a function to have an attribute?

A function should have some input, some local variables to compute
temporary results and a return value, I think nothing more...
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Re: why memoizing is faster

[eryksun ()]

On Friday, March 25, 2011 6:53:48 AM UTC-4, Andrea Crotti wrote:
>
> I had never seen such a thing, but why would this make sense at all?
> When does it make sense logically for a function to have an attribute?
> 
> A function should have some input, some local variables to compute
> temporary results and a return value, I think nothing more...

See Pep 232: http://www.python.org/dev/peps/pep-0232

Also, see the discussion thread on Python-Dev:

http://mail.python.org/pipermail/python-dev/2000-April/thread.html#3282

I don't think self-referenced static variables (as in C's "static" declaration) 
are discussed as a use case. Nonetheless, I've seen it done. For example:

http://stackoverflow.com/questions/338101/python-function-attributes-uses-and-abuses/338420#338420
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python 2.7.1 "serial" vs "pyserial"

[bruce bushby]

Hi

Is there any difference between the "serial" module in Python 2.7.1 and
"pyserial 2.5" ?

I can "import serial" without any issuesbut when I follow code examples
my scripts complain:
"TypeError: readline() takes no keyword arguments"

However lots of scripts
"import serial"
and then
"ser.readline(size=None, eol=chr(13))"

 . whereas I can only
"ser.readline()"
without any keywords or arguments.

Thanks
Bruce
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Re: why memoizing is faster

[Andrea Crotti]

"eryksun ()"  writes:
> See Pep 232: http://www.python.org/dev/peps/pep-0232
>
> Also, see the discussion thread on Python-Dev:
>
> http://mail.python.org/pipermail/python-dev/2000-April/thread.html#3282
>
> I don't think self-referenced static variables (as in C's "static"
> declaration) are discussed as a use case. Nonetheless, I've seen it
> done. For example:
>
> http://stackoverflow.com/questions/338101/python-function-attributes-uses-and-abuses/338420#338420

Ah ok I see the PEP, but actually it's a bit strange that in the PEP
they don't include any effective possible use of it, isn't it?

They normally always have some examples of why and what you can do with
it.
And by the way the first link is broken in the pep
http://www.neustar.biz/python/workshops/1998-11/proceedings/papers/aycock-little/aycock-little.html

Where should that be notified?
I was wondering some time ago, but big knowledge bases like this should
not have some kind of "check_validity_of_links" function, which checks
if you really get something from the pages that you link to?
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Re: dynamic assigments

[Seldon]

On 03/25/2011 12:05 AM, Steven D'Aprano wrote:

On Thu, 24 Mar 2011 19:39:21 +0100, Seldon wrote:


Hi, I have a question about generating variable assignments dynamically.

[...]

Now, I would like to use data contained in this list to dynamically
generate assignments of the form "var1 = value1", ecc where var1 is an
identifier equal (as a string) to the 'var1' in the list.


Why on earth would you want to do that?



Because I'm in this situation.  My current code is of the form:

var1 = func(arg=value1, *args)
..
varn = func(arg=valuen, *args)

where var1,..varn are variable names I know in advance and 
value1,..valuen are objects known in advance, too; func is a long 
invocation to a factory function.  Each invocation differs only for the 
value of the 'arg' argument, so I have a lot of boilerplate code I'd 
prefer to get rid of (for readability reasons).


I thought to refactor the code in a more declarative way, like

assignment_list = (
('var1', value1),
('var2', value2),
.. ,
)

for (variable, value) in assignment_list:
locals()[variable] = func(arg=value, *args)

My question is: what's possibly wrong with respect to this approach ?
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Re: Guido rethinking removal of cmp from sort method

[Antoon Pardon]

On Fri, Mar 25, 2011 at 11:05:17AM +0100, Stefan Behnel wrote:
> Antoon Pardon, 25.03.2011 10:21:
> >On Thu, Mar 24, 2011 at 11:49:53PM +, Steven D'Aprano wrote:
> >>On Thu, 24 Mar 2011 17:47:05 +0100, Antoon Pardon wrote:
> >>
> >>>However since that seems to be a problem for you I will be more
> >>>detailed. The original poster didn't ask for cases in which cmp was
> >>>necessary, he asked for cases in which not using cmp was cumbersome.
> >>
> >>I'm the original poster, and that's not what I said. I said:
> >>
> >>"If anyone has any use-cases for sorting with a comparison function that
> >>either can't be written using a key function, or that perform really
> >>badly when done so, this would be a good time to speak up."
> >>
> >>You'll notice that I said nothing about whether writing the code was easy
> >>or cumbersome, and nothing about readability.
> >
> >Well fine. I should have realised the question was just a pretense and that
> >there really never was any intention to consider the reactions, because
> >the answer is already fixed.
> 
> I don't think it is. It's just not as simple as "see, I have an
> artificial use case here, so you *must* put the feature back in the
> language".

Look we are provided with the cmp_to_key function. If something doesn't work
with that function or performs realy bad with that function, it means either
the function has a bug in it or something the function relies on, has a bug
in it. In either case you just fix the bug.

My guess is that cmp_to_key is implemented similarly as my example below.
So we simply have a constant overhead before we call the user provided
cmp function on the items to be sorted. So if this would fail to sort the
items or started to perform really badly (more than can be expected
by the overhead illustrated below) it would indicate an internal python
problem, either in the implementation of cmp_to_key or elsewhere.

Well if python has an internal problem, my expectation is that they will
fix the problem, instead of providing a cmp argument to sort as a work around.
So the outcome was fixed from the beginning.


def cmp_to_key(func):

  class cmpkey:
def __init__(self, arg):
  self.data = arg
  self.cmp = func

  def __lt__(self, other):
return self.cmp(self.data, other.data) < 0

  def __le__(self, other):
return self.cmp(self.data, other.data) <= 0

  ...

  return cmpkey
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Re: Reading/Writing files

[Ethan Furman]

On 3/18/2011 6:25 PM, Dan Stromberg wrote:


On Fri, Mar 18, 2011 at 4:00 PM, Ethan Furman mailto:et...@stoneleaf.us>> wrote:

Dan Stromberg wrote:


Are you on windows?

You probably should use / as your directory separator in Python,
not \.  In Python, and most other programming languages, \
starts an escape sequence, so to introduce a literal \, you
either need to prefix your string with r (r"\foo\bar") or double
your backslashes ("\\foo\\bar").

/ works fine on windows, and doesn't require escaping ("/foo/bar").


Depends on your definition of 'fine'.

--> from glob import glob
--> from pprint import pprint as pp
--> pp(glob('c:/temp/*.pdf'))
['c:/temp\\choose_python.pdf',
'c:/temp\\COA.pdf',
'c:/temp\\job_setup.pdf']

Visually ugly, and a pain to compare files and paths.


I argue that the first is quite a bit more readable than the second:
'c:/temp/choose_python.pdf'
os.path.join([ 'c:', 'temp', 'choose_python.pdf' ])


I agree with your argument, but think that
r'c:\temp\choose_python.pdf'
is even more readable still.  (Also, it wasn't I that suggested using
os.path.join() on everything.)



Also, heard of os.path.normpath?  You probably shouldn't compare
pathnames without it.


Thanks -- I've heard of it (mostly in the context of resolving relative 
path names (.. and such)), never checked it out... I'll read up on it.


~Ethan~
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Re: dynamic assigments

[Jean-Michel Pichavant]

Seldon wrote:

On 03/25/2011 12:05 AM, Steven D'Aprano wrote:

On Thu, 24 Mar 2011 19:39:21 +0100, Seldon wrote:

Hi, I have a question about generating variable assignments 
dynamically.

[...]

Now, I would like to use data contained in this list to dynamically
generate assignments of the form "var1 = value1", ecc where var1 is an
identifier equal (as a string) to the 'var1' in the list.


Why on earth would you want to do that?



Because I'm in this situation.  My current code is of the form:

var1 = func(arg=value1, *args)
..
varn = func(arg=valuen, *args)

where var1,..varn are variable names I know in advance and 
value1,..valuen are objects known in advance, too; func is a long 
invocation to a factory function.  Each invocation differs only for 
the value of the 'arg' argument, so I have a lot of boilerplate code 
I'd prefer to get rid of (for readability reasons).


I thought to refactor the code in a more declarative way, like

assignment_list = (
('var1', value1),
('var2', value2),
.. ,
)

for (variable, value) in assignment_list:
locals()[variable] = func(arg=value, *args)

My question is: what's possibly wrong with respect to this approach ?

First thing, locals help states the following:
"Note The contents of this dictionary should not be modified; changes 
may not affect the values of local and free variables used by the 
interpreter"


http://docs.python.org/library/functions.html#locals

Can't you use something like

rootValues = { 'var1': 45, 'var2': 0, }

def func2x(x):
   return x*2

def main():
   mappedValues = {}
   for varName in rootValues:
   mappedValues[varName] = func2x(rootValues[varName])
   print  mappedValues[varName]

main()

> 90
> 0


JM
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Re: dynamic assigments

[Michael Torrie]

On 03/25/2011 06:29 AM, Seldon wrote:
> Because I'm in this situation.  My current code is of the form:
> 
> var1 = func(arg=value1, *args)
> ..
> varn = func(arg=valuen, *args)
> 
> where var1,..varn are variable names I know in advance and 
> value1,..valuen are objects known in advance, too; func is a long 
> invocation to a factory function.  Each invocation differs only for the 
> value of the 'arg' argument, so I have a lot of boilerplate code I'd 
> prefer to get rid of (for readability reasons).
> 
> I thought to refactor the code in a more declarative way, like
> 
> assignment_list = (
> ('var1', value1),
> ('var2', value2),
> .. ,
> )
> 
> for (variable, value) in assignment_list:
>   locals()[variable] = func(arg=value, *args)
> 
> My question is: what's possibly wrong with respect to this approach ?

Wouldn't it be easiest just to keep the variables in a dictionary or
something, and then refer to them by key?

funcs = {}
for (variable, value) in assignment_list:
funcs[variable] = func(arg=value, *args)

print funcs['var1']

There doesn't seem to be any benefit to having things in the python
namespace when for your purposes a dictionary would work very cleanly.
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Re: dynamic assigments

[Jean-Michel Pichavant]

Jean-Michel Pichavant wrote:

Seldon wrote:

On 03/25/2011 12:05 AM, Steven D'Aprano wrote:

On Thu, 24 Mar 2011 19:39:21 +0100, Seldon wrote:

Hi, I have a question about generating variable assignments 
dynamically.

[...]

Now, I would like to use data contained in this list to dynamically
generate assignments of the form "var1 = value1", ecc where var1 is an
identifier equal (as a string) to the 'var1' in the list.


Why on earth would you want to do that?



Because I'm in this situation.  My current code is of the form:

var1 = func(arg=value1, *args)
..
varn = func(arg=valuen, *args)

where var1,..varn are variable names I know in advance and 
value1,..valuen are objects known in advance, too; func is a long 
invocation to a factory function.  Each invocation differs only for 
the value of the 'arg' argument, so I have a lot of boilerplate code 
I'd prefer to get rid of (for readability reasons).


I thought to refactor the code in a more declarative way, like

assignment_list = (
('var1', value1),
('var2', value2),
.. ,
)

for (variable, value) in assignment_list:
locals()[variable] = func(arg=value, *args)

My question is: what's possibly wrong with respect to this approach ?

First thing, locals help states the following:
"Note The contents of this dictionary should not be modified; changes 
may not affect the values of local and free variables used by the 
interpreter"


http://docs.python.org/library/functions.html#locals

Can't you use something like

rootValues = { 'var1': 45, 'var2': 0, }

def func2x(x):
   return x*2

def main():
   mappedValues = {}
   for varName in rootValues:
   mappedValues[varName] = func2x(rootValues[varName])
   print  mappedValues[varName]

main()

> 90
> 0


JM

could be simplified to the minmum with

rootValues = [45, 0]
anyFunc = lambda x:2x
var1, var2 = [anyFunc(value) for value in rootValues ]

JM
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Re: Guido rethinking removal of cmp from sort method

[Westley Martínez]

On Fri, 2011-03-25 at 07:11 +0100, Stefan Behnel wrote:
> Steven D'Aprano, 25.03.2011 06:46:
> > On Thu, 24 Mar 2011 18:32:11 -0700, Carl Banks wrote:
> >
> >> It's probably the least justified builtin other than pow.
> >
> > I don't know about that. Correctly, efficiently and *quickly*
> > implementing the three-argument version of pow is exactly the sort of
> > thing that should be in the built-ins, or at least the standard library.
> 
> I think that touches it already. We have a "math" module, so why is there a 
> *builtin* for doing special math? How much code is there really that only 
> uses pow() and does not import "math"?
> 
> Stefan
> 

pow() and math.pow() are different.

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Re: Reading/Writing files

[Westley Martínez]

On Fri, 2011-03-25 at 05:39 -0700, Ethan Furman wrote:
> On 3/18/2011 6:25 PM, Dan Stromberg wrote:
> >
> > On Fri, Mar 18, 2011 at 4:00 PM, Ethan Furman  > > wrote:
> >
> > Dan Stromberg wrote:
> >
> >
> > Are you on windows?
> >
> > You probably should use / as your directory separator in Python,
> > not \.  In Python, and most other programming languages, \
> > starts an escape sequence, so to introduce a literal \, you
> > either need to prefix your string with r (r"\foo\bar") or double
> > your backslashes ("\\foo\\bar").
> >
> > / works fine on windows, and doesn't require escaping ("/foo/bar").
> >
> >
> > Depends on your definition of 'fine'.
> >
> > --> from glob import glob
> > --> from pprint import pprint as pp
> > --> pp(glob('c:/temp/*.pdf'))
> > ['c:/temp\\choose_python.pdf',
> > 'c:/temp\\COA.pdf',
> > 'c:/temp\\job_setup.pdf']
> >
> > Visually ugly, and a pain to compare files and paths.
> >
> >
> > I argue that the first is quite a bit more readable than the second:
> > 'c:/temp/choose_python.pdf'
> > os.path.join([ 'c:', 'temp', 'choose_python.pdf' ])
> 
> I agree with your argument, but think that
>  r'c:\temp\choose_python.pdf'
> is even more readable still.  (Also, it wasn't I that suggested using
> os.path.join() on everything.)
> 
> 
> > Also, heard of os.path.normpath?  You probably shouldn't compare
> > pathnames without it.
> 
> Thanks -- I've heard of it (mostly in the context of resolving relative 
> path names (.. and such)), never checked it out... I'll read up on it.
> 
> ~Ethan~

Yes, readability counts, but so does platform independence.

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Re: Guido rethinking removal of cmp from sort method

[Stefan Behnel]

Westley Martínez, 25.03.2011 14:39:

On Fri, 2011-03-25 at 07:11 +0100, Stefan Behnel wrote:

Steven D'Aprano, 25.03.2011 06:46:

On Thu, 24 Mar 2011 18:32:11 -0700, Carl Banks wrote:


It's probably the least justified builtin other than pow.


I don't know about that. Correctly, efficiently and *quickly*
implementing the three-argument version of pow is exactly the sort of
thing that should be in the built-ins, or at least the standard library.


I think that touches it already. We have a "math" module, so why is there a
*builtin* for doing special math? How much code is there really that only
uses pow() and does not import "math"?


pow() and math.pow() are different.


I don't find that a good excuse for pow() being a builtin. Why not just 
rename it to "math.powmod" instead?


Stefan

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jump to C definition

[Andrea Crotti]

While I use emacs, if it knows where the source code is, I can very
easily jump to a function definition even if it's in C.

I think it would be nice to have something like this also for python, at
least to make it easy to explore the code and learn something new,
without digging too much into the many files and directories.

I can easily see the function definition from ipython of everything
which is written in python, but no way to have access to the C code.

Is there anything already implemented/working in this direction?

Thanks,
Andrea
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Re: "in house" pypi?

[Colin J. Williams]

On 24-Mar-11 03:13 AM, John Nagle wrote:

On 3/23/2011 8:19 PM, Miki Tebeka wrote:

Greetings,

My company want to distribute Python packages internally. We would
like something like an internal PyPi where people can upload and
easy_install from packages.

Is there such a ready made solution? I'd like something as simple as
possible, without my install headache.

Thanks, -- Miki


PyPi isn't a code repository, like CPAN or SourceForge.
It's mostly a collection of links.

Take a look at CPAN, Perl's package repository. That's
well organized and useful. Modules are stored in a common archive
after an approval process, and can be downloaded and installed
in a standard way.

"easy_install" generally isn't easy. It has some built-in
assumptions about where things are stored, assumptions which
often don't hold true.

John Nagle


I've not found problems with "easy_install" using Windows.

Colin W.

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Writing to a file

[jyoung79]

Just curious how others view the 2 examples below for creating and 
writing to a file in Python (in OS X).  Is one way better than the other?  
If it was a large amount of text, would the 'os.system' call be a bad 
way to do it?

Thanks.

Jay


>>> f = open('~/Desktop/test.txt', 'w')
>>> f.write('testing 1... 2... 3...')
>>> f.close()
>>> 
>>> 
>>> import os
>>> os.system('echo "Testing a... b... c..." > "~/Desktop/test2.txt"')
0
>>> 

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Converting an array of string to array of float

[joy99]

Dear Group,

I got a question which might be possible but I am not getting how to
do it.

If I have a list, named,
list1=[1.0,2.3,4.4,5.5]

Now each element in the array holds the string property if I want to
convert them to float, how would I do it?

Extracting the values with for and appending to a blank list it would
not solve the problem. If appended to a blank list, it would not
change the property.

If any one of the learned members can kindly suggest any solution?

Thanks in advance.
Best Regards,
Subhabrata.
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Re: Converting an array of string to array of float

[Nitin Pawar]

did you try type casting with float ?

On Fri, Mar 25, 2011 at 8:49 PM, joy99  wrote:

> Dear Group,
>
> I got a question which might be possible but I am not getting how to
> do it.
>
> If I have a list, named,
> list1=[1.0,2.3,4.4,5.5]
>
> Now each element in the array holds the string property if I want to
> convert them to float, how would I do it?
>
> Extracting the values with for and appending to a blank list it would
> not solve the problem. If appended to a blank list, it would not
> change the property.
>
> If any one of the learned members can kindly suggest any solution?
>
> Thanks in advance.
> Best Regards,
> Subhabrata.
> --
> http://mail.python.org/mailman/listinfo/python-list
>



-- 
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Re: Converting an array of string to array of float

[Jason Swails]

I'm guessing you have something like

list1=['1.0', '2.3', '4.4', '5.5', ...], right?

You can do this:

for i in range(len(list1)):
  list1[i] = float(list1[i])

There's almost certainly a 1-liner you can use, but this should work.

--Jason

On Fri, Mar 25, 2011 at 8:19 AM, joy99  wrote:

> Dear Group,
>
> I got a question which might be possible but I am not getting how to
> do it.
>
> If I have a list, named,
> list1=[1.0,2.3,4.4,5.5]
>
> Now each element in the array holds the string property if I want to
> convert them to float, how would I do it?
>
> Extracting the values with for and appending to a blank list it would
> not solve the problem. If appended to a blank list, it would not
> change the property.
>
> If any one of the learned members can kindly suggest any solution?
>
> Thanks in advance.
> Best Regards,
> Subhabrata.
> --
> http://mail.python.org/mailman/listinfo/python-list
>
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Re: Writing to a file

[cassiope]

On Mar 25, 8:07 am,  wrote:
> Just curious how others view the 2 examples below for creating and
> writing to a file in Python (in OS X).  Is one way better than the other?  
> If it was a large amount of text, would the 'os.system' call be a bad
> way to do it?
>
> Thanks.
>
> Jay
>
>
>
> >>> f = open('~/Desktop/test.txt', 'w')
> >>> f.write('testing 1... 2... 3...')
> >>> f.close()
>
> >>> import os
> >>> os.system('echo "Testing a... b... c..." > "~/Desktop/test2.txt"')
> 0
>
>

I personally consider each use of os.system(..) as something that
needs to be eliminated.
Maybe 'echo' isn't too bad... but (for example) is it subject to
limited argument lengths?
Does it perform differently on different OSs?  And if it's not
something intrinsic to the
OS, might there be 'PATH' issues: where is the called program?
Finally, there may be
some security issues (in general) though perhaps not in your specific
example.

Of course, if speed is a real issue there may be some value in
buffering a long string
before using whatever method to save it in a file.  OTOH these
functions usually include
system buffering (which the incremental os.system(..) call clearly
won't have).

Hope that helps...
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Re: Converting an array of string to array of float

[Christoph Brand]

If you want to have it even shorter and you are using Python 2.5 or 
greater you can also use:

list1 = [float(list_item) for list_item in list1]

Am 25.03.2011 16:27, schrieb Jason Swails:

I'm guessing you have something like

list1=['1.0', '2.3', '4.4', '5.5', ...], right?

You can do this:

for i in range(len(list1)):
  list1[i] = float(list1[i])

There's almost certainly a 1-liner you can use, but this should work.

--Jason

On Fri, Mar 25, 2011 at 8:19 AM, joy99 > wrote:


Dear Group,

I got a question which might be possible but I am not getting how to
do it.

If I have a list, named,
list1=[1.0,2.3,4.4,5.5]

Now each element in the array holds the string property if I want to
convert them to float, how would I do it?

Extracting the values with for and appending to a blank list it would
not solve the problem. If appended to a blank list, it would not
change the property.

If any one of the learned members can kindly suggest any solution?

Thanks in advance.
Best Regards,
Subhabrata.
--
http://mail.python.org/mailman/listinfo/python-list



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Re: Converting an array of string to array of float

[Blockheads Oi Oi]

On 25/03/2011 15:27, Jason Swails wrote:

I'm guessing you have something like

list1=['1.0', '2.3', '4.4', '5.5', ...], right?

You can do this:

for i in range(len(list1)):
   list1[i] = float(list1[i])



or

for i, x in enumerate(list1):
list1[i] = float(x)


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Re: Converting an array of string to array of float

[Rafael Durán Castañeda]

But you must be sure that the list only contains objects than can be
converted into float, if not you'll get:

>>> float('something')
Traceback (most recent call last):
  File "", line 1, in 
float('something')
ValueError: could not convert string to float: something
>>>

2011/3/25 Blockheads Oi Oi 

> On 25/03/2011 15:27, Jason Swails wrote:
>
>> I'm guessing you have something like
>>
>> list1=['1.0', '2.3', '4.4', '5.5', ...], right?
>>
>> You can do this:
>>
>> for i in range(len(list1)):
>>   list1[i] = float(list1[i])
>>
>>
> or
>
> for i, x in enumerate(list1):
>list1[i] = float(x)
>
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>
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embedding interactive python interpreter

[Eric Frederich]

I am able to embed the interactive Python interpreter in my C program
except that when the interpreter exits, my entire program exits.

#include 
#include 

int main(int argc, char *argv[]){
printf("line %d\n", __LINE__);
Py_Initialize();
printf("line %d\n", __LINE__);
Py_Main(argc, argv);
printf("line %d\n", __LINE__);
Py_Finalize();
printf("line %d\n", __LINE__);
return 0;
}

When I run the resulting binary I get the following

$ ./embedded_python
line 5
line 7
Python 2.7.1 (r271:86832, Mar 25 2011, 11:56:07)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-48)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> print 'hi'
hi
>>> exit()


I never see line 9 or 11 printed.
I need to embed python in an application that needs to do some cleanup
at the end so I need that code to execute.
What am I doing wrong?

Is there something else I should call besides "exit()" from within the
interpreter?
Is there something other than Py_Main that I should be calling?

Thanks,
~Eric
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Re: Writing to a file

[John Gordon]

In   
writes:

> Just curious how others view the 2 examples below for creating and 
> writing to a file in Python (in OS X).  Is one way better than the other?  
> If it was a large amount of text, would the 'os.system' call be a bad 
> way to do it?

The write() way is much better.  (However, I'm not sure it will do what
you were expecting with the tilde in the file path.)

-- 
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: Writing to a file

[Adam Tauno Williams]

On Fri, 2011-03-25 at 15:07 +, jyoun...@kc.rr.com wrote:
> Just curious how others view the 2 examples below for creating and 
> writing to a file in Python (in OS X).  Is one way better than the other?  
> If it was a large amount of text, would the 'os.system' call be a bad 
> way to do it?

Option#1

> >>> f = open('~/Desktop/test.txt', 'w')
> >>> f.write('testing 1... 2... 3...')
> >>> f.close()

Option#2

> >>> import os
> >>> os.system('echo "Testing a... b... c..." > "~/Desktop/test2.txt"')

Option#2 is weird and stupid.  

If something goes wrong making sense the error message in Option#2 is
going to be much harder than Option#1 - where opening the file in write
mode, and writing the file are discrete operations.  Also Option#2 is
going to be far more platform dependent, even shell dependent [Where
does "echo" come from?  What does "~" mean?].

Do things in discrete steps, and be explicit about what you are doing.
Option#2 fails both those requirements.

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Re: Converting an array of string to array of float

[Blockheads Oi Oi]

On 25/03/2011 15:46, Rafael Durán Castañeda wrote:

But you must be sure that the list only contains objects than can be
converted into float, if not you'll get:

 >>> float('something')
Traceback (most recent call last):
   File "", line 1, in 
 float('something')
ValueError: could not convert string to float: something


You learn something new every day :)

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Re: Converting an array of string to array of float

[bruno.desthuilli...@gmail.com]

On 25 mar, 16:19, joy99  wrote:
> Dear Group,
>
> I got a question which might be possible but I am not getting how to
> do it.
>
> If I have a list, named,
> list1=[1.0,2.3,4.4,5.5]
>
> Now each element in the array holds the string property if I want to
> convert them to float, how would I do it?
>
> Extracting the values with for and appending to a blank list it would
> not solve the problem. If appended to a blank list, it would not
> change the property.
>
> If any one of the learned members can kindly suggest any solution?
>


>>> print source
['0.0', '1.0', '2.0', '3.0', '4.0', '5.0', '6.0', '7.0', '8.0', '9.0']
>>> source[:] = map(float, source)
>>> print source
[0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0]
>>>

Note the "source[:] = " part - it modifies the list in place.

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Re: Converting an array of string to array of float

[joy99]

On Mar 25, 9:19 pm, "bruno.desthuilli...@gmail.com"
 wrote:
> On 25 mar, 16:19, joy99  wrote:
>
>
>
> > Dear Group,
>
> > I got a question which might be possible but I am not getting how to
> > do it.
>
> > If I have a list, named,
> > list1=[1.0,2.3,4.4,5.5]
>
> > Now each element in the array holds the string property if I want to
> > convert them to float, how would I do it?
>
> > Extracting the values with for and appending to a blank list it would
> > not solve the problem. If appended to a blank list, it would not
> > change the property.
>
> > If any one of the learned members can kindly suggest any solution?
>
> >>> print source
>
> ['0.0', '1.0', '2.0', '3.0', '4.0', '5.0', '6.0', '7.0', '8.0', '9.0']>>> 
> source[:] = map(float, source)
> >>> print source
>
> [0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0]
>
>
>
> Note the "source[:] = " part - it modifies the list in place.

Thanks Bruno. I just missed it. I got it back and thanks Blockhead for
giving me new angle to look into the problem.
Best Regards,
Subhabrata.
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Re: embedding interactive python interpreter

[Eric Frederich]

So I found that if I type ctrl-d then the other lines will print.

It must be a bug then that the exit() function doesn't do the same thing.
The documentation says "The return value will be the integer passed to
the sys.exit() function" but clearly nothing is returned since the
call to Py_Main exits rather than returning (even when calling
sys.exit instead of just exit).

In the mean time is there a way to redefine the exit function in
Python to do the same behavior as "ctrl-d?"
I realize that in doing that (if its even possible) still won't
provide a way to pass a value back from the interpreter via sys.exit.

Thanks,
~Eric



On Fri, Mar 25, 2011 at 12:02 PM, Eric Frederich
 wrote:
> I am able to embed the interactive Python interpreter in my C program
> except that when the interpreter exits, my entire program exits.
>
>    #include 
>    #include 
>
>    int main(int argc, char *argv[]){
>        printf("line %d\n", __LINE__);
>        Py_Initialize();
>        printf("line %d\n", __LINE__);
>        Py_Main(argc, argv);
>        printf("line %d\n", __LINE__);
>        Py_Finalize();
>        printf("line %d\n", __LINE__);
>        return 0;
>    }
>
> When I run the resulting binary I get the following
>
> $ ./embedded_python
> line 5
> line 7
> Python 2.7.1 (r271:86832, Mar 25 2011, 11:56:07)
> [GCC 4.1.2 20080704 (Red Hat 4.1.2-48)] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
 print 'hi'
> hi
 exit()
>
>
> I never see line 9 or 11 printed.
> I need to embed python in an application that needs to do some cleanup
> at the end so I need that code to execute.
> What am I doing wrong?
>
> Is there something else I should call besides "exit()" from within the
> interpreter?
> Is there something other than Py_Main that I should be calling?
>
> Thanks,
> ~Eric
>
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Re: embedding interactive python interpreter

[MRAB]

On 25/03/2011 17:37, Eric Frederich wrote:

So I found that if I type ctrl-d then the other lines will print.

It must be a bug then that the exit() function doesn't do the same thing.
The documentation says "The return value will be the integer passed to
the sys.exit() function" but clearly nothing is returned since the
call to Py_Main exits rather than returning (even when calling
sys.exit instead of just exit).

In the mean time is there a way to redefine the exit function in
Python to do the same behavior as "ctrl-d?"
I realize that in doing that (if its even possible) still won't
provide a way to pass a value back from the interpreter via sys.exit.


You could flush stdout after each print or turn off buffering on stdout
with:

setvbuf(stdout, NULL, _IONBF, 0);


Thanks,
~Eric



On Fri, Mar 25, 2011 at 12:02 PM, Eric Frederich
  wrote:

I am able to embed the interactive Python interpreter in my C program
except that when the interpreter exits, my entire program exits.

#include
#include

int main(int argc, char *argv[]){
printf("line %d\n", __LINE__);
Py_Initialize();
printf("line %d\n", __LINE__);
Py_Main(argc, argv);
printf("line %d\n", __LINE__);
Py_Finalize();
printf("line %d\n", __LINE__);
return 0;
}

When I run the resulting binary I get the following

$ ./embedded_python
line 5
line 7
Python 2.7.1 (r271:86832, Mar 25 2011, 11:56:07)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-48)] on linux2
Type "help", "copyright", "credits" or "license" for more information.

print 'hi'

hi

exit()



I never see line 9 or 11 printed.
I need to embed python in an application that needs to do some cleanup
at the end so I need that code to execute.
What am I doing wrong?

Is there something else I should call besides "exit()" from within the
interpreter?
Is there something other than Py_Main that I should be calling?

Thanks,
~Eric



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Re: embedding interactive python interpreter

[Eric Frederich]

Added a fflush(stdout) after each printf and, as I expectedstill
only the first 2 prints.


On Fri, Mar 25, 2011 at 1:47 PM, MRAB  wrote:
> On 25/03/2011 17:37, Eric Frederich wrote:
>>
>> So I found that if I type ctrl-d then the other lines will print.
>>
>> It must be a bug then that the exit() function doesn't do the same thing.
>> The documentation says "The return value will be the integer passed to
>> the sys.exit() function" but clearly nothing is returned since the
>> call to Py_Main exits rather than returning (even when calling
>> sys.exit instead of just exit).
>>
>> In the mean time is there a way to redefine the exit function in
>> Python to do the same behavior as "ctrl-d?"
>> I realize that in doing that (if its even possible) still won't
>> provide a way to pass a value back from the interpreter via sys.exit.
>>
> You could flush stdout after each print or turn off buffering on stdout
> with:
>
>    setvbuf(stdout, NULL, _IONBF, 0);
>
>> Thanks,
>> ~Eric
>>
>>
>>
>> On Fri, Mar 25, 2011 at 12:02 PM, Eric Frederich
>>   wrote:
>>>
>>> I am able to embed the interactive Python interpreter in my C program
>>> except that when the interpreter exits, my entire program exits.
>>>
>>>    #include
>>>    #include
>>>
>>>    int main(int argc, char *argv[]){
>>>        printf("line %d\n", __LINE__);
>>>        Py_Initialize();
>>>        printf("line %d\n", __LINE__);
>>>        Py_Main(argc, argv);
>>>        printf("line %d\n", __LINE__);
>>>        Py_Finalize();
>>>        printf("line %d\n", __LINE__);
>>>        return 0;
>>>    }
>>>
>>> When I run the resulting binary I get the following
>>>
>>> $ ./embedded_python
>>> line 5
>>> line 7
>>> Python 2.7.1 (r271:86832, Mar 25 2011, 11:56:07)
>>> [GCC 4.1.2 20080704 (Red Hat 4.1.2-48)] on linux2
>>> Type "help", "copyright", "credits" or "license" for more information.
>>
>> print 'hi'
>>>
>>> hi
>>
>> exit()
>>>
>>>
>>> I never see line 9 or 11 printed.
>>> I need to embed python in an application that needs to do some cleanup
>>> at the end so I need that code to execute.
>>> What am I doing wrong?
>>>
>>> Is there something else I should call besides "exit()" from within the
>>> interpreter?
>>> Is there something other than Py_Main that I should be calling?
>>>
>>> Thanks,
>>> ~Eric
>>>
>
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>
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Re: dynamic assigments

[Carl Banks]

On Mar 25, 5:29 am, Seldon  wrote:
> I thought to refactor the code in a more declarative way, like
>
> assignment_list = (
> ('var1', value1),
> ('var2', value2),
> .. ,
> )
>
> for (variable, value) in assignment_list:
>         locals()[variable] = func(arg=value, *args)

Someday we'll get through a thread like this without anyone mistakenly
suggesting the use of locals() for this


> My question is: what's possibly wrong with respect to this approach ?

I'll answer this question assuming you meant, "hypothetically, if it
actually worked".

The thing that's wrong with your "declarative way" is that it adds
nothing except obscurity.  Just do this:

var1 = value2
var2 = value2

What you're trying to do is akin to writing poetry, or a sociological
research paper.  The emphasis in that kind of writing is not on clear
communication of ideas, but on evoking some emotion with the form of
the words (almost always at the expense of clear communication).

Same thing with your "declarative way".  It adds nothing to the code
apart from a feeling of formalism.  It doesn't save you any work: you
still have to type out all the variables and values.  It doesn't save
you from repeating yourself.  It doesn't minimize the possibility of
typos or errors; quite the opposite.  It DOES make your code a lot
harder to read.

So stick with regular assignments.


"But wait," you say, "what if I don't know the variable names?"


Well, if you don't know the variable names, how can you write a
function that uses those names as local variables?


"Er, well I can access them with locals() still."


You should be using a dictionary, then.

I have found that whenever I thought I wanted to dynamically assign
local variables, it turned out I also wanted to access them
dynamically, too.  Therefore, I would say that any urge to do this
should always be treated as a red flag that you should be using a
dictionary.


"Ok, but say I do know what the variables are, but for some reason I'm
being passed a huge list of these key,value pairs, and my code
consists of lots and lots of formulas and with lots of these
variables, so it'd be unwieldy to access them through a dictionary or
as object attributes, not to mention a lot slower."


Ah, now we're getting somewhere.  This is the main use case for
dynamically binding local variables in Python, IMO.  You're getting a
big list of variables via some dynamic mechanism, you know what the
variables are, and you want to operate on them as locals, but you also
want to avoid boilerplate of binding all of them explicitly.

Not a common use case, but it happens.  (I've faced it several times,
but the things I work on make it more common for me.  I bit the bullet
and wrote out the boilerplate.)


Carl Banks
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Re: Reading/Writing files

[Dan Stromberg]

On Fri, Mar 25, 2011 at 6:42 AM, Westley Martínez wrote:

>
> > > I argue that the first is quite a bit more readable than the second:
> > > 'c:/temp/choose_python.pdf'
> > > os.path.join([ 'c:', 'temp', 'choose_python.pdf' ])
> >
> > I agree with your argument, but think that
> >  r'c:\temp\choose_python.pdf'
> > is even more readable still.  (Also, it wasn't I that suggested using
> > os.path.join() on everything.)
> >
> >
> > > Also, heard of os.path.normpath?  You probably shouldn't compare
> > > pathnames without it.
> >
> > Thanks -- I've heard of it (mostly in the context of resolving relative
> > path names (.. and such)), never checked it out... I'll read up on it.
> >
> > ~Ethan~
>
> Yes, readability counts, but so does platform independence.
>

Last I heard, Python _defined_ forward slash in a pathname as a legal
directory separator - so as long as you normpath when using a pathname so
constructed on its way out of Python and on to the user or external command
(via cmd.exe, command.com, etc.), you are (or were) supposed to be fine.
It's been some time since I heard that though.  References:

http://stackoverflow.com/questions/1607751/how-to-create-a-file-one-directory-up

http://bytes.com/topic/python/answers/23123-when-did-windows-start-accepting-forward-slash-path-separator

http://stackoverflow.com/questions/3020267/how-to-make-a-python-or-perl-script-portable-to-both-linux-and-windows

>From lib/libos.text in the CPython 2.4 source code:
\begin{datadesc}{altsep}
An alternative character used by the operating system to separate pathname
components, or \code{None} if only one separator character exists.  This is
set to \character{/} on Windows systems where \code{sep} is a
backslash.
Also available via \module{os.path}.
\end{datadesc}

And I must confess, those references aren't as convincing as I'd expected.

I don't see anything documenting this behavior beyond it happening to work
fine on *ix and Windows, but I'm just about sure I saw it stated previously
on this mailing list before, that / was legal in Python as a directory
separator on all platforms.

'shame I don't have a MacOS 9, VMS or RiscOS system to test on...  Any
takers?

I'd actually go so far as to say that if only *ix (including MacOS X) and
Windows Python are fine with it, that's not really enough - because I
certainly hope someday there'll be something better than these that Python
will run well on.
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Re: why memoizing is faster

[Terry Reedy]

On 3/25/2011 4:49 AM, Andrea Crotti wrote:

Terry Reedy  writes:

def fib_iter(n, _cache = [1,1]):
   k = len(_cache)
   if n>= k:
 for i in range(k, n+1):
_cache.append(_cache[i-2] + _cache[i-1])
   return _cache[n]


I just realized that the signature really ought to be
def fib_iter(n, *, _cache = [1,1]):
so that the _cache parameter is keyword only (relatively new feature), 
so that it cannot be overwritten by accident but only by intentional 
resetting of what by its name is obviously intended to be a private, do 
not touch value. This pretty much eliminates one objection people have 
had to this sort of thing.


Actually, it should be
  def fib_iter(n, *, _cache = [0,1]):
to match the standard definition that fib(0)=0, etc.
https://secure.wikimedia.org/wikipedia/en/wiki/Fibonacci_number
I just happened to copy the your initialization.
People who omit 0 from the series also usually leave fib(0) undefined.


If it had a more "expected" behaviour of instantiating a new cache
dictionary every time this trick would not be possible.


Next time someone claims that mutable defaults are not useful, I will 
try to remember to show this example again.


--
Terry Jan Reedy

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Re: why memoizing is faster

[Terry Reedy]

On 3/25/2011 5:16 AM, Stefan Behnel wrote:


Terry's version is playing with the fact that default arguments are only
instantiated once, i.e. (unless overridden by passing an explicit
argument) the "_cache" is shared over all calls to the function. This is
similar to what your memoization decorator does, but without the
additional dict. And, it also "suffers" from the same timing problem
that I mentioned before.


It depends on what one wants to measure. If one is memoizing because one 
expects to call the function 1000s of times in some program, then the 
fast lookup time of repeated calls represents the actual 
post-initialization burden on that program. If one want to measure the 
initialization time, then the cache can easily be restarted with each 
call (once one knows how): fib_iter(100,_cache=[0,1])


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Re: python 2.7.1 "serial" vs "pyserial"

[Terry Reedy]

On 3/25/2011 7:27 AM, bruce bushby wrote:

Hi

Is there any difference between the "serial" module in Python 2.7.1 and
"pyserial 2.5" ?


When asking about 3rd party modules, it may help to give a reference to 
the site or download page on pypi. (And one should also check to package 
specific lists or help address.) For anything like i/o that interacts 
with the system, specifying platform/os may also help.



I can "import serial" without any issuesbut when I follow code
examples my scripts complain:
"TypeError: readline() takes no keyword arguments"


Actual code and traceback may help anyone to respond.


However lots of scripts
"import serial"
and then
"ser.readline(size=None, eol=chr(13))"


This would not execute. Did you mean serial.readline...?

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Where to put .pth files on slax

[Tim Johnson]

Hello: I'm trying to put together a test platform on a slax OS.
Python 2.7 packages appear to be at /user/lib/python2.7.

Where is the appropriate place to put a .pth file?

Note, I have django on this system too, but slax does not resolved
system paths. And that is 'slax' not 'slack'.
-- 
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Dump interpreter history?

[Ken D'Ambrosio]

Hey, all.  A co-worker asked me a question, and I've got no idea how (or
if) it can be done.  Bottom line: he'd like to save off the text from an
interpreter session, his thinking being that you've already tried to get
what you want, and now you just need to gussy it up in an editor.

Can this be done?

Thanks!

-Ken




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Re: Dump interpreter history?

[Brian Curtin]

On Fri, Mar 25, 2011 at 16:03, Ken D'Ambrosio  wrote:

> Hey, all.  A co-worker asked me a question, and I've got no idea how (or
> if) it can be done.  Bottom line: he'd like to save off the text from an
> interpreter session, his thinking being that you've already tried to get
> what you want, and now you just need to gussy it up in an editor.
>
> Can this be done?
>
> Thanks!
>
> -Ken


If readline is available, this might be a helpful start:
http://my.opera.com/alecmg/blog/2007/03/30/add-history-and-completion-to-python-in
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Re: Dump interpreter history?

[FELD Boris]

Take a look at : 
http://ipython.scipy.org/doc/manual/html/interactive/tutorial.html#use-your-input-history

Cheers,
FELD Boris

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FELD Boris
Sent with Sparrow
On vendredi 25 mars 2011 at 22:03, Ken D'Ambrosio wrote: 
> Hey, all. A co-worker asked me a question, and I've got no idea how (or
> if) it can be done. Bottom line: he'd like to save off the text from an
> interpreter session, his thinking being that you've already tried to get
> what you want, and now you just need to gussy it up in an editor.
> 
> Can this be done?
> 
> Thanks!
> 
> -Ken
> 
> 
> 
> 
> -- 
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> 
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Re: Dump interpreter history?

[John Gordon]

In  "Ken D'Ambrosio" 
 writes:

> Hey, all.  A co-worker asked me a question, and I've got no idea how (or
> if) it can be done.  Bottom line: he'd like to save off the text from an
> interpreter session, his thinking being that you've already tried to get
> what you want, and now you just need to gussy it up in an editor.

If you're running on a unix system, run the "script" command before
starting the interpreter.  Then when you're finished with the interpreter,
type "exit" to end the script session.  This will create a file named
"typescript" containing all of the input and output which occurred.

-- 
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: Dump interpreter history?

[Daniel Mahoney]

On Fri, 25 Mar 2011 17:03:55 -0400, Ken D'Ambrosio wrote:

> Hey, all.  A co-worker asked me a question, and I've got no idea how (or
> if) it can be done.  Bottom line: he'd like to save off the text from an
> interpreter session, his thinking being that you've already tried to get
> what you want, and now you just need to gussy it up in an editor.
> 
> Can this be done?
> 
> Thanks!
> 
> -Ken

import readline
readline.write_history_file([filename])

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Re: Dump interpreter history?

[Calvin Spealman]

Tell your coworker that what he should be doing is writing good tests,
which he can rerun repeatedly while working towards a solution.
Instead of writing a new function in an interpreter, he can add tests
to confirm how he wants it to behave and then keep working on it unitl
those tests pass.

On Fri, Mar 25, 2011 at 5:03 PM, Ken D'Ambrosio  wrote:
> Hey, all.  A co-worker asked me a question, and I've got no idea how (or
> if) it can be done.  Bottom line: he'd like to save off the text from an
> interpreter session, his thinking being that you've already tried to get
> what you want, and now you just need to gussy it up in an editor.
>
> Can this be done?
>
> Thanks!
>
> -Ken
>
>
>
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>



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Re: Guido rethinking removal of cmp from sort method

[Steven D'Aprano]

On Fri, 25 Mar 2011 10:21:35 +0100, Antoon Pardon wrote:

> On Thu, Mar 24, 2011 at 11:49:53PM +, Steven D'Aprano wrote:
>> On Thu, 24 Mar 2011 17:47:05 +0100, Antoon Pardon wrote:
>> 
>> > However since that seems to be a problem for you I will be more
>> > detailed. The original poster didn't ask for cases in which cmp was
>> > necessary, he asked for cases in which not using cmp was cumbersome.
>> 
>> I'm the original poster, and that's not what I said. I said:
>> 
>> "If anyone has any use-cases for sorting with a comparison function
>> that either can't be written using a key function, or that perform
>> really badly when done so, this would be a good time to speak up."
>> 
>> You'll notice that I said nothing about whether writing the code was
>> easy or cumbersome, and nothing about readability.
> 
> Well fine. I should have realised the question was just a pretense and
> that there really never was any intention to consider the reactions,
> because the answer is already fixed. Of course a key function can always
> be written, it may just need a specific class to implement the specific
> order. Likewise there is no reason to expect the order-functions to
> preform worse when implemented in a class, rather than in a function.

The reason Guido is considering re-introducing cmp is that somebody at 
Google approached him with a use-case where a key-based sort did not 
work. The use-case was that the user had masses of data, too much data 
for the added overhead of Decorate-Sort-Undecorate (which is what key 
does), but didn't care if it took a day or two to sort.

So there is at least one use-case for preferring slowly sorting with a 
comparison function over key-based sorting. I asked if there any others. 
It seems not.



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Re: dynamic assigments

[Steven D'Aprano]

On Fri, 25 Mar 2011 02:47:04 -0700, scattered wrote:

> I specified that the cipher text consists of characters in the range A
> to Z (note the case). 

So you did. My apologies.


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Re: Converting an array of string to array of float

[Steven D'Aprano]

On Fri, 25 Mar 2011 08:19:24 -0700, joy99 wrote:

> Dear Group,
> 
> I got a question which might be possible but I am not getting how to do
> it.
> 
> If I have a list, named,
> list1=[1.0,2.3,4.4,5.5]

That looks like a list of floats already. Perhaps you meant:

list1 = ["1.0", "2.3", "4.4", "5.5"]

Notice that the elements are now strings, not floats.


> Now each element in the array holds the string property if I want to
> convert them to float, how would I do it?
> 
> Extracting the values with for and appending to a blank list it would
> not solve the problem. If appended to a blank list, it would not change
> the property.

I don't understand what you mean. You want to get a list of floats. You 
create a list of floats. How does that not solve the problem?

Wait, do you mean you want to change them *in-place*? Like this:


>>> alist = ["1.1", "2.2", "3.3", "4.4", "5.5"]
>>> blist = alist  # reference to the same list object
>>> alist[:] = map(float, alist)
>>> print(blist[0] + 1)  # prove that it is an in-place change
2.1


The key is the slice assignment: map(float, alist) creates a new list, 
but the assignment alist[:] = ... stores those values in the original 
list, instead of just binding the name to a new object. It is equivalent 
to this:

temp = map(float, alist)
del alist[:]  # empty the list in place
alist.extend(temp)
del temp  # delete the variable

only easier and faster.


If you don't like map(), you can use a list comprehension:

alist[:] = [float(s) for s in alist]


Finally, if your list is so truly astonishingly huge that you don't have 
room for it and the list-of-floats at the same time, hundreds of millions 
of items or more, then you can change the list items in place:

for i, s in enumerate(alist):
alist[i] = float(s)


But for small lists and merely large lists (millions or tens of millions) 
of items, this will probably be much slower than the solutions shown 
above. But your MMV -- time your code and find out for yourself.


-- 
Steven
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Re: Guido rethinking removal of cmp from sort method

[Steven D'Aprano]

On Fri, 25 Mar 2011 13:56:23 +0100, Antoon Pardon wrote:

> Look we are provided with the cmp_to_key function. If something doesn't
> work with that function or performs realy bad with that function, it
> means either the function has a bug in it or something the function
> relies on, has a bug in it. In either case you just fix the bug.

No, it means that the trade-offs made by cmp_to_key, or by sorting with a 
key function, do not interact well with what you are trying to do.

An analogy: Python lists are contiguous arrays of pointers. When the 
array is full, Python automatically doubles the size of the list. This is 
a good trade-off of space (memory) for time, because it means that list 
access is O(1), searching is O(N), and appending is O(1) on average. At 
worst, you waste 50% of the memory used, which is pretty good.

But if you're programming for a device with 8 K of memory (if such a 
thing even exists these days!), this would be a *terrible* strategy. 
(Python wouldn't even fit in 8K, but never mind that...) In this case, 
memory is more precious than programmer convenience, or even execution 
speed. It's not enough to hand-wave and say "Python lists have a bug that 
needs fixing", because that's simply not the case. It's that the design 
of Python lists doesn't suit the use-case, and if you try it, it will 
perform badly or not at all: by design, Python lists assume memory will 
be plentiful and time will be short.

That is exactly the same trade-off key-based sorting makes: it uses more 
memory to speed up sorting. This is a good strategy for Python, because 
Python already requires lots of memory (so no major loss there), and is a 
rather slow language (so speed-ups help).

So the question is, being completely general, as there any *real-world* 
(not artificial, made-up) uses where sorting with a comparison function 
works but a key function doesn't? I'm not limiting you to cases where you 
have a shortage of memory but lots of time available. There may be other 
design choices where key-based sorting sucks. We already know that some 
people just prefer the look and feel of writing and using cmp functions. 
Is there anything else?



-- 
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Re: dynamic assigments

[Steven D'Aprano]

On Fri, 25 Mar 2011 13:29:20 +0100, Seldon wrote:

> On 03/25/2011 12:05 AM, Steven D'Aprano wrote:
>> On Thu, 24 Mar 2011 19:39:21 +0100, Seldon wrote:
>>
>>> Hi, I have a question about generating variable assignments
>>> dynamically.
>> [...]
>>> Now, I would like to use data contained in this list to dynamically
>>> generate assignments of the form "var1 = value1", ecc where var1 is an
>>> identifier equal (as a string) to the 'var1' in the list.
>>
>> Why on earth would you want to do that?
>>
>>
> Because I'm in this situation.  My current code is of the form:
> 
> var1 = func(arg=value1, *args)
> ..
> varn = func(arg=valuen, *args)
> 
> where var1,..varn are variable names I know in advance and
> value1,..valuen are objects known in advance, too; func is a long
> invocation to a factory function.  Each invocation differs only for the
> value of the 'arg' argument, so I have a lot of boilerplate code I'd
> prefer to get rid of (for readability reasons).


If you *truly* need all those variables, and can't re-design your code to 
be simpler and neater, then you're stuck with an uncomfortable choice 
between:

(1) Tedious boilerplate

(2) If using global variables, you can inject new variables into the 
global namespace using globals()[name] = value

(3) If using local variables, and you trust the data (you better, you 
wrote it!), then you can't use locals() but you can use exec, at 
considerable cost of speed. (By my testing, a call to exec is about ten 
times slower than a direct execution of the same source code.)

All three are bad code-smells. They tell me that you probably should re-
think your algorithm to have less reliance on named variables created 
with a "long invocation to a factory function" -- particularly if they 
differ only by a single parameter.

But, if you can't change your design, I'd prefer the tedious boilerplate 
of (1) over (3), and prefer (2) only if it involved multiple dozens of 
variables. For half a dozen, or even two dozen, I'd stick to the 
boilerplate. Yes, it sucks, but that's because the design sucks, and not 
every piece of code is destined to be a thing of beauty.

The reason that I would prefer tedious boilerplate is twofold:

- Although it's a code-smell, it's less of a smell than exec or the use 
of global variables. You read code more than you write it: I'd rather the 
pain of writing the boilerplate once, than the continual "Hmmm, what's 
this nonsense then?" of reading it over and over again.

- If you ever change the design, say the variables no longer differ in 
just one argument to the factory function, but a variable number of them, 
it's probably easier to change the boilerplate than it is to change the 
other two solutions. They're relatively inflexible without a lot of work, 
so boilerplate, as ugly as it is, is probably the safer and more 
conservative (less "clever") solution.


Hope this helps.




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Re: Guido rethinking removal of cmp from sort method

[Carl Banks]

On Mar 25, 3:06 pm, Steven D'Aprano  wrote:
> The reason Guido is considering re-introducing cmp is that somebody at
> Google approached him with a use-case where a key-based sort did not
> work. The use-case was that the user had masses of data, too much data
> for the added overhead of Decorate-Sort-Undecorate (which is what key
> does), but didn't care if it took a day or two to sort.
>
> So there is at least one use-case for preferring slowly sorting with a
> comparison function over key-based sorting. I asked if there any others.
> It seems not.

1. You asked for a specific kind of use case.  Antoon gave you a use
case, you told him that wasn't the kind of use case you were asking
for, then you turn around and say "I guess there are no use
cases" (without the mentioning qualification).


2. I posted two use cases in this thread that fit your criteria, and
you followed up to that subthread so you most likely read them.  Here
they are again so you won't overlook them this time:

"You have are given an obscure string collating function implented in
a C library you don't have the source to."  (Fits your criterion
"can't be done with key=".)

"I'm sitting at an interactive session and I have a
convenient cmp function but no convenient key, and I care more about
the four minutes it'd take to whip up a clever key function or an
adapter class than the 0.2 seconds I'd save to on sorting
time."  (Fits your criterion "performs really badly when done so".)


3. You evidently also overlooked the use-case example posted on Python-
dev that you followed up to.


Call me crazy, but you seem to be overlooking a lot of things in your
zeal to prove your point.


Carl Banks
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Re: Converting an array of string to array of float

[Algis Kabaila]

On Saturday 26 March 2011 02:27:12 Jason Swails wrote:
> I'm guessing you have something like
> 
> list1=['1.0', '2.3', '4.4', '5.5', ...], right?
> 
> You can do this:
> 
> for i in range(len(list1)):
>   list1[i] = float(list1[i])

Better,

list1 = [float(v) for v in list1]

One statement only - long live list comprehension!

OldAl.
> 
> There's almost certainly a 1-liner you can use, but this
> should work.
> 
> --Jason
> 
> On Fri, Mar 25, 2011 at 8:19 AM, joy99 
 wrote:
> > Dear Group,
> > 
> > I got a question which might be possible but I am not
> > getting how to do it.
> > 
> > If I have a list, named,
> > list1=[1.0,2.3,4.4,5.5]
> > 
> > Now each element in the array holds the string property if
> > I want to convert them to float, how would I do it?
> > 
> > Extracting the values with for and appending to a blank
> > list it would not solve the problem. If appended to a
> > blank list, it would not change the property.
> > 
> > If any one of the learned members can kindly suggest any
> > solution?
> > 
> > Thanks in advance.
> > Best Regards,
> > Subhabrata.
> > --
> > http://mail.python.org/mailman/listinfo/python-list

-- 
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http://akabaila.pcug.org.au/StructuralAnalysis.pdf
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Re: Guido rethinking removal of cmp from sort method

[Dan Stromberg]

On Sun, Mar 13, 2011 at 5:59 AM, Steven D'Aprano <
steve+comp.lang.pyt...@pearwood.info> wrote:

> The removal of cmp from the sort method of lists is probably the most
> disliked change in Python 3. On the python-dev mailing list at the
> moment, Guido is considering whether or not it was a mistake.
>
> If anyone has any use-cases for sorting with a comparison function that
> either can't be written using a key function, or that perform really
> badly when done so, this would be a good time to speak up


The point of increased memory use seems possibly relevant.  I tried to test
for that yesterday using some big lists of tuples of floats, and didn't see
it having much significance (if anything the cmp version seemed to take More
memory), but it might merit further study, as it'll be a while before cell
phones (and refrigerators) have an excess of memory - and I very much want
to run Python on my cell phone (and wouldn't mind it on my fridge).

There's also the issue of a lazy comparison function, that I don't seem to
have gotten a response to - if you have a Very expensive comparison
operation involving megabytes or even gigabytes of data, and want to perform
just enough of it to get the job done, how does one do this with a key
comparator and no cmp comparator?  It seems like you could almost do it by
using a generator for your key comparator, but it also seems like the stuff
in memory would add up really (too) fast.  This program has an example:
http://stromberg.dnsalias.org/~strombrg/equivalence-classes.html#python
(The version at the following URL might be a little newer)
http://stromberg.dnsalias.org/cgi-bin/viewvc.cgi/equivalence-classes/trunk/equivs2-python/?root=svn
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Re: python 2.7.1 "serial" vs "pyserial"

[eryksun ()]

On 3/25/2011 7:27 AM, bruce bushby wrote:
>
> Is there any difference between the "serial" module in Python 2.7.1 and
> "pyserial 2.5" ?

I've never used it, but "pyserial" is actually "serial": 

http://pyserial.sourceforge.net

I have it installed on my system via Christoph Gohlke's "Base" distribution. 
AFAIK, it's not in the standard install of Python 2.7. 

> However lots of scripts
> "import serial"
> and then
> "ser.readline(size=None, eol=chr(13))"

That's odd that it says keywords aren't supported. The method signature is 

def readline(self, size=None, eol=LF):

This is from the FileLike class in serialutil.py, line 141 here:

http://pyserial.svn.sourceforge.net/viewvc/pyserial/trunk/pyserial/serial/serialutil.py?revision=398&view=markup

Are you sure you're not using an actual 'file' object? The latter's readline 
method takes a size argument, but as a regular positional argument.
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Re: Converting an array of string to array of float

[Blockheads Oi Oi]

Thanks Bruno. I just missed it. I got it back and thanks Blockhead for
giving me new angle to look into the problem.
Best Regards,
Subhabrata.


Nothing personal, but it's Blockheads (plural) AND you missed the OI OI. 
 What is the problem with modern day education? :)



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Re: Where to put .pth files on slax

[Tim Johnson]

* Tim Johnson  [110325 12:59]:
> Hello: I'm trying to put together a test platform on a slax OS.
> Python 2.7 packages appear to be at /user/lib/python2.7.
> 
> Where is the appropriate place to put a .pth file?
  I must have stumped the chumps. And this chump hasn't used
 pth files in a coon's age. I just used the PYTHONPATH environment
 variable. 
 ---
 Solved.
 ---

> Note, I have django on this system too, but slax does not resolved
> system paths. And that is 'slax' not 'slack'.
> -- 
> Tim 
> tim at johnsons-web dot com or akwebsoft dot com
> http://www.akwebsoft.com
> -- 
> http://mail.python.org/mailman/listinfo/python-list

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tim at johnsons-web dot com or akwebsoft dot com
http://www.akwebsoft.com
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Re: Dump interpreter history?

[Dan Mahoney]

Yeah, sorry about that. The square brackets were supposed to indicate that
filename is an optional argument. If not supplied, defaults to .history.

Dan Mahoney
catd...@gmail.com

Sent from my Android phone

On Mar 25, 2011 6:57 PM, "Tim Chase"  wrote:

On 03/25/2011 04:40 PM, Daniel Mahoney wrote:

> On Fri, 25 Mar 2011 17:03:55 -0400, Ken D'Ambrosio wrote:
>
>  Hey, all.  A co-worker asked me a question, and I've got no idea how (or
>> if) it can be done.  Bottom line: he'd like to save off the text from an
>> interpreter session, his thinking being that you've already tried to get
>> what you want, and now you just need to gussy it up in an editor.
>>
>
> import readline
> readline.write_history_file([filename])
>

Just to clarify (I thought Daniel's answer was so easy it must have
misinterpreted the OP's request), that's a single string as a filename, not
a list containing a filename.  I tried

 filename = 'output.txt'
 import readline
 readline.write_history_file([filename])

and got a traceback about the expected parameter type.  For clarity, it
should have been

 readline.write_history_file(filename)

or

 readline.write_history_file('output.txt')

But otherwise, Daniel's given a dead-easy solution.

-tkc
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Re: Writing to a file

[eryksun ()]

On Friday, March 25, 2011 11:07:19 AM UTC-4, jyou...@kc.rr.com wrote:
>
> >>> f = open('~/Desktop/test.txt', 'w')
> >>> f.write('testing 1... 2... 3...')
> >>> f.close()

Consider using "with" to automatically close the file and os.path for 
cross-platform compatibility:

import os.path
user_home = os.path.expanduser('~')
test_absname = os.path.join(user_home, 'Desktop', 'test.txt')

with open(test_absname, 'w') as test:
test.write('testing 1... 2... 3...')

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Re: Writing to a file

[Littlefield, Tyler]

>with open(test_absname, 'w') as test:
what's the difference in that and test = ...? I can see why you 
mentioned the os.path for cross-platform, but I don't understand why 
someone would use with over =.

On 3/25/2011 7:11 PM, eryksun () wrote:

On Friday, March 25, 2011 11:07:19 AM UTC-4, jyou...@kc.rr.com wrote:

f = open('~/Desktop/test.txt', 'w')
f.write('testing 1... 2... 3...')
f.close()

Consider using "with" to automatically close the file and os.path for 
cross-platform compatibility:

 import os.path
 user_home = os.path.expanduser('~')
 test_absname = os.path.join(user_home, 'Desktop', 'test.txt')

 with open(test_absname, 'w') as test:
 test.write('testing 1... 2... 3...')




--

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Ty

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Re: Writing to a file

[Gregory Ewing]

John Gordon wrote:


The write() way is much better.  (However, I'm not sure it will do what
you were expecting with the tilde in the file path.)


It won't, but the os.path.expanduser() function can
be used to fix that.

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Re: Writing to a file

[Gregory Ewing]

jyoun...@kc.rr.com wrote:


import os
os.system('echo "Testing a... b... c..." > "~/Desktop/test2.txt"')


This is like going out the back door, getting a ladder out of
the shed and climbing through your bedroom window to get into
bed at night, instead of just using the stairs.

Use open/write/close. It's much more direct and efficient.

--
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Re: Dump interpreter history?

[Tim Chase]

On 03/25/2011 04:40 PM, Daniel Mahoney wrote:

On Fri, 25 Mar 2011 17:03:55 -0400, Ken D'Ambrosio wrote:


Hey, all.  A co-worker asked me a question, and I've got no idea how (or
if) it can be done.  Bottom line: he'd like to save off the text from an
interpreter session, his thinking being that you've already tried to get
what you want, and now you just need to gussy it up in an editor.


import readline
readline.write_history_file([filename])


Just to clarify (I thought Daniel's answer was so easy it must 
have misinterpreted the OP's request), that's a single string as 
a filename, not a list containing a filename.  I tried


  filename = 'output.txt'
  import readline
  readline.write_history_file([filename])

and got a traceback about the expected parameter type.  For 
clarity, it should have been


  readline.write_history_file(filename)

or

  readline.write_history_file('output.txt')

But otherwise, Daniel's given a dead-easy solution.

-tkc


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Re: Writing to a file

[Dan Stromberg]

with closes the file for you, when the indented block is exited.

~ isn't cross-platform at all, in fact it's not precisely python, though
os.path.expanduser understands it.

AFAIK, the jury's still out on whether the /'s in pathnames as directory
separators are portable.  I know they work on *ix and Windows (in API's
since DOS 2.0 when a directory hierarchy was introduced), but what about
Python on MacOS 9, VMS, RiscOS, etcetera?  I heard years ago on
comp.lang.python that Python (not just the underlying OS, as above, but
Python too) would treat / as a directory separator irrespective of what the
underlying OS thought of it, but I'm having difficulty finding more than
tangential references to this idea now.

On Fri, Mar 25, 2011 at 6:39 PM, Littlefield, Tyler wrote:

> >with open(test_absname, 'w') as test:
> what's the difference in that and test = ...? I can see why you mentioned
> the os.path for cross-platform, but I don't understand why someone would use
> with over =.
>
> On 3/25/2011 7:11 PM, eryksun () wrote:
>
>> On Friday, March 25, 2011 11:07:19 AM UTC-4, jyou...@kc.rr.com wrote:
>>
>>> f = open('~/Desktop/test.txt', 'w')
>> f.write('testing 1... 2... 3...')
>> f.close()
>>
> Consider using "with" to automatically close the file and os.path for
>> cross-platform compatibility:
>>
>> import os.path
>> user_home = os.path.expanduser('~')
>> test_absname = os.path.join(user_home, 'Desktop', 'test.txt')
>>
>> with open(test_absname, 'w') as test:
>> test.write('testing 1... 2... 3...')
>
>
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C Callback Function using ctypes

[OJ]

Hi I am opening a shared library which has defined the following
callback prototype:
extern void DebugMessage(int level, const char *message, ...);

My implementation in Python looks like this:
DEBUGFUNC = ctypes.CFUNCTYPE(None, ctypes.c_int, ctypes.POINTER(ctypes.c_char))
def DebugMessage(lvl, msg):
print lvl, msg
return
debug_callback = DEBUGFUNC(DebugMessage)

Which gives me the following when running my python script:
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 

How can I get something useful?

If I change the print to:
print lvl, msg[0], it produces an Segfault
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Re: Writing to a file

[eryksun ()]

On Friday, March 25, 2011 9:39:11 PM UTC-4, Littlefield, Tyler wrote:
> >with open(test_absname, 'w') as test:
> what's the difference in that and test = ...? I can see why you 
> mentioned the os.path for cross-platform, but I don't understand why 
> someone would use with over =.

It avoids having to write a try...finally block to close the file automatically 
and immediately in case of an error. Also, you can easily chain additional 
context managers into this syntax, such as for redirecting standard 
input/output to the file. More info here:

http://diveintopython3.org/files.html
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best python games?

[sogeking99]

hey guys, what are some of the best games made in python? free games
really. like pygames stuff. i want to see what python is capable of.

cant see any good one on pygames site really, though they have nothing
like sort by rating or most downloaded as far as i can tell
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passing c_void_p to an library(.so) to c function

[OJ]

Hi
I am trying to implement a python frontend for a c library. I can open
the library successfully and call functions using ctypes. My challenge
now is that this library are using plugins, which is also libraries
(.so on linux).

The library function for adding these plugins expects a viod * to the
plugin. Here is what I have so far:

main = ctypes.cdll.LoadLibrary(libpath) # This is the main library
plugin = ctypes.cdll.LoadLibrary(filename) # This is the plugin
print '%s' % (plugin)
rval = main.CoreAttachPlugin(2, None)

The above example produces:


In this case I get no error message, but this is with the void * =
NULL, so the plugin is not attached. I have tried different thing to
pass the void *.

Test 1:
rval = main.CoreAttachPlugin(2, plugin)


Traceback (most recent call last):
  File "./m64p.py", line 171, in 
rval = m64p.CoreAttachPlugin(i, plugin)
ctypes.ArgumentError: argument 2: : Don't
know how to convert parameter 2


Test 2:
rval = main.CoreAttachPlugin(2, plugin._handle)


Segmentation fault

Test 3:
rval = main.CoreAttachPlugin(2, ctypes.byref(plugin))


Traceback (most recent call last):
  File "./m64p.py", line 171, in 
rval = m64p.CoreAttachPlugin(i, ctypes.byref(plugin))
TypeError: byref() argument must be a ctypes instance, not 'CDLL'

Does anyone have some tips to how I can do what I want :)?
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Re: best python games?

[Corey Richardson]

On 03/25/2011 10:39 PM, sogeking99 wrote:
> hey guys, what are some of the best games made in python? free games
> really. like pygames stuff. i want to see what python is capable of.
> 
> cant see any good one on pygames site really, though they have nothing
> like sort by rating or most downloaded as far as i can tell

Unknown Horizons is pretty OK, and the upcoming PARPG looks promising
(both use the FIFE engine).

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Re: historic grail python browser "semi-recovered"

[Juno]

Hi, Luke Leighton...

Maybe I can help...

... Mugs

Globe Life Insurance
$1* Buys $50,000 Life Insurance. Adults or Children. No Medical Exam.
http://thirdpartyoffers.juno.com/TGL3141/4d8d53ea5a2d5414007st02duc-- 
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Re: why memoizing is faster

[Stefan Behnel]

Terry Reedy, 25.03.2011 21:18:

On 3/25/2011 5:16 AM, Stefan Behnel wrote:


Terry's version is playing with the fact that default arguments are only
instantiated once, i.e. (unless overridden by passing an explicit
argument) the "_cache" is shared over all calls to the function. This is
similar to what your memoization decorator does, but without the
additional dict. And, it also "suffers" from the same timing problem
that I mentioned before.


It depends on what one wants to measure. If one is memoizing because one
expects to call the function 1000s of times in some program, then the fast
lookup time of repeated calls represents the actual post-initialization
burden on that program. If one want to measure the initialization time,
then the cache can easily be restarted with each call (once one knows how):
fib_iter(100,_cache=[0,1])


Not "restarted" in the sense that it gets cleaned up, though. The above 
simply passes an explicit value for it that will be used for the single 
call. Future calls won't be affected.


Stefan

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Re: best python games?

[Dan Stromberg]

On Fri, Mar 25, 2011 at 7:39 PM, sogeking99  wrote:

> hey guys, what are some of the best games made in python? free games
> really. like pygames stuff. i want to see what python is capable of.
>
> cant see any good one on pygames site really, though they have nothing
> like sort by rating or most downloaded as far as i can tell
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>


Define "best game"...  This simple two word phrase can mean many different
things to many different people.

I'd say today's dominant "military drill as entertainment" games are a bit
lacking in, well, game theory, even playability.

For a game that has stood the test of time for thousands of years, that's
got both simpler rules and more complex gameplay than western chess, that's
a perfect knowledge battle of two intellects, take a look at Go AKA Weiqi
AKA Baduk.

Some time ago, I put together a pygame interface to the gnugo AI.  It's at
http://stromberg.dnsalias.org/cgi-bin/viewvc.cgi/pggo/trunk/?root=svn&sortby=log

Don't judge the quality of the game by the quality of the interface though -
I'm aware the interface has problems with tracebacking on illegal moves
sometimes.  But for sheer depth of gameplay, there's perhaps nothing that
competes with Go.

And don't judge the game by the quality of the gnugo AI either - the game
has a large amount more complexity and depth than gnugo is aware of;
although gnugo is rather impressive as a software project, the problem it's
trying to solve is exceptionally vast.  On the other hand, gnugo can easily
trounce newbies.

BTW, Go makes an excellent proving ground for new AI techniques, because of
its simple rules and emergent complexity.

Oh, and if you try it, watch out: A former coworker once described Go as
"intellectual cocaine".  It can eat up a surprising amount of your time once
you really get into it.  There are people who study it (and little else) for
an entire lifetime without  truly mastering it.

Finally, Go has an excellent handicap system that allows a newbie to play an
expert without horribly distorted gameplay.  This attribute alone makes it
pretty interesting.
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Re: why memoizing is faster

[Terry Reedy]

On 3/26/2011 12:17 AM, Stefan Behnel wrote:


Not "restarted" in the sense that it gets cleaned up, though. The above
simply passes an explicit value for it that will be used for the single
call.


Which satisfies the time test need, but...

> Future calls won't be affected.

Good point. If one does fib(1) and wants to dump the cache without 
dumping all references to the function object, one can currently do

  fib_iter.__kwdefaults__['_cache'] = [0,1]
to truly reset the cache, at least with CPython.

--
Terry Jan Reedy

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