Python style: to check or not to check args and data members

[Bruno Desthuilliers]

Paul Rubin a écrit :
> Bruno Desthuilliers <onurb at xiludom.gro> writes:
> 
>>I've rarely encoutered "silent" data corruption with Python - FWIW, I
>>once had such a problem, but with a lower-level statically typed
>>language (integer overflow), and I was a very newbie programmer by that
>>time. Usually, one *very quickly* notices when something goes wrong.
> 
> 
> The same thing can happen in Python, and the resulting bugs can be
> pretty subtle.  I noticed the following example as the result of
> another thread, which was about how to sort an 85 gigabyte file.
> Try to put a slice interface on a file-based object and you can
> hit strange integer-overflow bugs once the file gets larger than 2GB:
> 
>     Python 2.3.4 (#1, Feb  2 2005, 12:11:53) 
>     [GCC 3.4.2 20041017 (Red Hat 3.4.2-6.fc3)] on linux2
>     Type "help", "copyright", "credits" or "license" for more information.
>     >>> print slice(0, 3**33)
>     slice(0, 5559060566555523L, None)         # OK ...
> 
> So we expect slicing with large args to work properly.  But then:
> 
>     >>> class A:
>     ...   def __getitem__(self, s):
>     ...     print s
>     ... 
>     >>> a = A()
>     >>> a[0:3**33]
>     slice(0, 2147483647, None)                # oops!!!!
>     >>> 

Looks like a Python bug, not a programmer error. And BTW, it doesn't 
happens with >=2.4.1

Python 2.4.1 (#1, Jul 23 2005, 00:37:37)
[GCC 3.3.4 20040623 (Gentoo Linux 3.3.4-r1, ssp-3.3.2-2, pie-8.7.6)] on 
linux2
Type "help", "copyright", "credits" or "license" for more information.
 >>> print slice(0, 3**33)
slice(0, 5559060566555523L, None)
 >>> class A(object):
...     def __getitem__(self, s):
...             print s
...
 >>> A()[0:3**33]
slice(0, 5559060566555523L, None)
 >>>