== on object tests identity in 3.x
While discussing Python issue #12067 (http://bugs.python.org/issue12067#msg222442), I learned that Python 3.4 implements '==' and '!=' on the object type such that if no special equality test operations are implemented in derived classes, there is a default implementation that tests for identity (as opposed to equality of the values). The relevant code is in function do_richcompare() in Objects/object.c. IMHO, that default implementation contradicts the definition that '==' and '!=' test for equality of the values of an object. Python 2.x does not seem to have such a default implementation; == and != raise an exception if attempted on objects that don't implement equality in derived classes. I'd like to gather comments on this issue, specifically: -> Can someone please elaborate what the reason for that is? -> Where is the discrepancy between the documentation of == and its default implementation on object documented? To me, a sensible default implementation for == on object would be (in Python): if v is w: return True; elif type(v) != type(w): return False else: raise ValueError("Equality cannot be determined in default implementation") Andy
participants (10)
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Andreas Maier
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Benjamin Peterson
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Chris Angelico
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Ethan Furman
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Jan Kaliszewski
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Rob Cliffe
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Stephen J. Turnbull
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Steven D'Aprano
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Terry Reedy
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Xavier Morel