[Python-Dev] NotImplemented comparisons

[Georg Brandl]

Facundo Batista schrieb:
> 2007/8/2, Guido van Rossum <guido at python.org>:
> 
>> NonImplemented isn't treated as special when returned by __cmp__();
>> __cmp__ is not considered a binary operator like __add__. (__lt__ and
>> friends *do* get treated as such -- but instead of __rlt__ we use
>> __gt__, etc.)
> 
> I understand that is tricky how NotImplemented and comparisons interact.
> 
> But how do you explain the difference in behaviour between Linux and Windows?

I now investigated that, and it seems that if you return NotImplemented from
a __cmp__() function, and the other's __cmp__() isn't helpful either, you end
up comparing the addresses of the objects (in your case c and None) -- the
outcome of which is not consistent across machines or sessions.


Georg


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