Stefan Halfpap wrote at 2020-2-5 14:57 +0100: >I do not understand the following statement from the python (2 and 3) >documentation regarding __hash__ and __eq__ methods: >"If a class does not define an __eq__() ><https://docs.python.org/3/reference/datamodel.html#object.__eq__> method it >should not define a __hash__() ><https://docs.python.org/3/reference/datamodel.html#object.__hash__> operation >either;” >(see https://docs.python.org/3/reference/datamodel.html#object.__hash__ ><https://docs.python.org/3/reference/datamodel.html#object.__hash__> ) > >I thought it relates to the second part (“if it defines __eq__() ><https://docs.python.org/3/reference/datamodel.html#object.__eq__> but not >__hash__() ><https://docs.python.org/3/reference/datamodel.html#object.__hash__>, its >instances will not be usable as items in hashable collections”), which is >totally clear to me. >But then the implication should be the other way around.
"if not A then not B" is equivalent to "if B then A". In your case: "__eq__ not defined, then __hash__ not defined" is equivalent to "__hash__ definied requires __eq__ defined". -- https://mail.python.org/mailman/listinfo/python-list
