On Fri, 22 Feb 2019 at 18:29, Serhiy Storchaka <storch...@gmail.com> wrote: > Should we add default implementations of __float__ and __complex__ when > either __index__ or __int__ is defined? Currently: > > >>> class A: > ... def __int__(self): return 42 > ... > >>> int(A()) > 42 > >>> float(A()) > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > TypeError: float() argument must be a string or a number, not 'A' > >>> complex(A()) > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > TypeError: complex() first argument must be a string or a number, not 'A' > > Or just document that in order to have a coherent integer type class, > when __index__() or __int__() are defined __float__() and __complex__() > should also be defined, and all should return equal values.
I think when __index__ is defined, it would be reasonable to have that imply the same floating point conversion rules as are applied for builtin ints, since the conversion is supposed to be lossless in that case (and if it isn't lossless, that's what `__int__` is for). However, I don't think the decision is quite as clearcut as it is for `__index__` implying `__int__`. Lossy conversions to int shouldn't imply anything about conversions to real numbers or floating point values. Cheers, Nick. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
