[Python-Dev] cmp(x,x) (original) (raw)

Raymond Hettinger python at rcn.com
Mon May 24 19:52:29 EDT 2004

[Bob Ippolito]

I think the use case mentioned was something like Numeric, where it may be useful for anArray == anotherArray to return an array of bool, not a single True or False

The code in question is in Py_RichCompareBool() which always just returns True or False. That routine is called by list.contains() and many other functions that expect a yes or no answer.

The regular rich comparison function, Py_RichCompare() is the same as it always was and can still return arrays of bools, complex numbers, or anything at all.

IOW, we're still looking for a use case that warrants removing the identity-implies-equality guarantee out of Py_RichCompareBool(). My argument focused on the invariant assumptions that would be broken if this was done. Second, I don't believe that a sane use case will be found for an object x that returns False for "bool(x==x)" and that returns False for "x in [x]". Stretching ones mind to find such an object seems like an exercise in masochism.

Raymond

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