None in string formatting

[rodney . maxwell]

Was doing some string formatting, noticed the following:

>>> x = None
>>> "%s" % x
'None'

Is there a reason it maps to 'None'? I had expected ''.

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Re: How to turn a variable name into a string?

[Rodney Maxwell]

> c = None  (result of an assignment after the os.environ.get()
returned a KeyError). 

Why not trap the KeyError?

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python.exe on Mac OS X!?

[Rodney Maxwell]

I did a source code build of Python 2.4.1 on OS X (10.3.8) and the
executable produced was 'python.exe'. Can someone tell me whether this
is a bug, feature, or UserError?

% ./configure

% make

% ./python.exe
Python 2.4.1 (#1, Apr 17 2005, 12:14:12)
[GCC 3.3 20030304 (Apple Computer, Inc. build 1495)] on darwin
>>>

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Re: python.exe on Mac OS X!?

[Rodney Maxwell]

>> executable produced was 'python.exe'. Can someone tell me whether
this
>> is a bug, feature, or UserError?

> I'm not sure. Why don't you grab the binary?

> http://www.python.org/ftp/python/2.4.1/MacPython-OSX-2.4.1-1 .dmg

Because I need to keep multiple versions of Python on this machine, and
as far as I can tell the binary installer overwrites the default
installed version.
I could be wrong.

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Re: python.exe on Mac OS X!?

[Rodney Maxwell]

> The default file system on MacOSX is case insensitive.  As a result
the .exe
> extension is required to disambiguate the generated executable from
the 
> Python directory in the source distro. 

OK. I got it.

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Why is 'None' not assignable but 'True'/'False' are?

[Rodney Maxwell]

In Python 2.4.1:

>>> None = 99
SyntaxError: assignment to None
>>> True = 99
>>> False = 99
>>> True == False
True
---
So why is 'None' special?

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Extended slicing and Ellipsis - where are they used?

[Rodney Maxwell]

The following are apparently legal Python syntactically:
   L[1:3, 8:10]
   L[1, ..., 5:-2]

But they don't seem to work on lists:
>>> l = [0,1,2,3]
>>> l[0:2,3]
Traceback (most recent call last):
  File "", line 1, in 
TypeError: list indices must be integers
>>> l[...]
Traceback (most recent call last):
  File "", line 1, in 
TypeError: list indices must be integers

So where is this extended slicing used?

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Re: Extended slicing and Ellipsis - where are they used?

[Rodney Maxwell]

On Sep 13, 5:50 pm, James Stroud <[EMAIL PROTECTED]> wrote:
> Rodney Maxwell wrote:
> > The following are apparently legal Python syntactically:
> >L[1:3, 8:10]
> >L[1, ..., 5:-2]
>
> > But they don't seem to work on lists:
> >>>> l = [0,1,2,3]
> >>>> l[0:2,3]
> > Traceback (most recent call last):
> >   File "", line 1, in 
> > TypeError: list indices must be integers
> >>>> l[...]
> > Traceback (most recent call last):
> >   File "", line 1, in 
> > TypeError: list indices must be integers
>
> > So where is this extended slicing used?
>
> AFAICT this syntax is not used in the standard library. However, the
> mega-beauty of it is that you can make use of it in your own classes:
>
> py> class Bob(list):
> ...   def __getitem__(self, i):
> ... try:
> ...   return [list.__getitem__(self, j) for j in i]
> ... except TypeError:
> ...   return list.__getitem__(self, i)
> ...
> py> b = Bob(xrange(15, 30))
> py> b[3, 5, 7, 13]
> [18, 20, 22, 28]
>
> James

Or
>>> b[0:3, 5, 9]
[[15, 16, 17], 20, 24]

which is what I was looking for in the first place.

Thanks,
Rodney

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Re: Extended slicing and Ellipsis - where are they used?

[Rodney Maxwell]

On Sep 13, 5:50 pm, James Stroud <[EMAIL PROTECTED]> wrote:
> Rodney Maxwell wrote:
> > The following are apparently legal Python syntactically:
> >L[1:3, 8:10]
> >L[1, ..., 5:-2]
>
> > But they don't seem to work on lists:
> >>>> l = [0,1,2,3]
> >>>> l[0:2,3]
> > Traceback (most recent call last):
> >   File "", line 1, in 
> > TypeError: list indices must be integers
> >>>> l[...]
> > Traceback (most recent call last):
> >   File "", line 1, in 
> > TypeError: list indices must be integers
>
> > So where is this extended slicing used?
>
> AFAICT this syntax is not used in the standard library. However, the
> mega-beauty of it is that you can make use of it in your own classes:
>
> py> class Bob(list):
> ...   def __getitem__(self, i):
> ... try:
> ...   return [list.__getitem__(self, j) for j in i]
> ... except TypeError:
> ...   return list.__getitem__(self, i)
> ...
> py> b = Bob(xrange(15, 30))
> py> b[3, 5, 7, 13]
> [18, 20, 22, 28]
>
> James

Or
>>> b[0:3, 5, 9]
[[15, 16, 17], 20, 24]

which is what I was looking for in the first place.

Thanks,
Rodney

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