Python style: to check or not to check args and data members
Sun Sep 3 06:38:57 CEST 2006
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()
slice(0, 2147483647, None) # oops!!!!
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