Annoying behaviour of the != operator

Jordan Rastrick jrastrick at student.usyd.edu.au
Wed Jun 8 21:36:37 CEST 2005


Well, I'll admit I haven't ever used the Numeric module, but since
PEP207 was submitted and accepted, with Numeric as apparently one of
its main motivations, I'm going to assume that the pros and cons for
having == and ilk return things other than True or False have already
been discussed at length and that argument settled. (I suppose theres a
reason why Numeric arrays weren't just given the same behaviour as
builtin lists, and then simple non-special named methods to do the
'rich' comparisons.)

But again, it seems like a pretty rare and marginal use case, compared
to simply wanting to see if some object a is equal to (in a non object
identity sense) object b.

The current situation seems to be essentially use __cmp__ for normal
cases, and use the rich operations, __eq__, __gt__, __ne__, and rest,
only in the rare cases. Also, if you define one of them, make sure you
define all of them.

Theres no room for the case of objects where the == and != operators
should return a simple True or False, and are always each others
complement, but <, >= and the rest give an error. I haven't written
enough Python to know for sure, but based on my experience in other
languages I'd guess this case is vastly more common than all others put
together.

I'd be prepared to bet that anyone defining just __eq__ on a class, but
none of __cmp__, __ne__, __gt__ etc, wants a != b to return the
negation of a.__eq__(b). It can't be any worse than the current case of
having == work as the method __eq__ method describes but != work by
object identity.

So far, I stand by my suggested change.




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