Rich Comparisons Gotcha

[Terry Reedy]

Rasmus Fogh wrote:
> Rhamphoryncus wrote:
>> You grossly overvalue using the "in" operator on lists.
> 
> Maybe. But there is more to it than just 'in'. If you do:
>>>> c = numpy.zeros((2,))
>>>> ll = [1, c, 3.]
> then the following all throw errors:
> 3 in ll, 3 not in ll, ll.index(3), ll.count(3), ll.remove(3)
> c in ll, c not in ll, ll.index(c), ll.count(c), ll.remove(c)
> 
> Note how the presence of c in the list makes it behave wrong for 3 as
> well.

So do not put numpy arrays into lists without wrapping them.  They were 
designed and semi-optimized, by a separate community, for a specific 
purpose -- numerical computation -- and not for 'playing nice' with 
other Python objects.

It is a design feature of Python that people can implement specialized 
objects with specialized behaviors for specialized purposes.