Serhiy Storchaka added the comment: I agree that by default calling reversed() on mapping should raise a TypeError. But for now issubclass(collections.abc.Mapping, typing.Reversible) returns False. If add default __reversed__ implementation this test will return True. We have to find other way to make Mapping true non-reversible in all meanings.
Perhaps there is a bug in typing.Reversible. It doesn't accept all types supported by reversed(). >>> class Counter(int): ... def __getitem__(s, i): return i ... def __len__(s): return s ... >>> list(reversed(Counter(10))) [9, 8, 7, 6, 5, 4, 3, 2, 1, 0] >>> issubclass(Counter, typing.Reversible) False And accepts types that don't work with reversed(). >>> class L(list): ... __reversed__ = None ... >>> reversed(L()) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'NoneType' object is not callable >>> issubclass(L, typing.Reversible) True ---------- nosy: +gvanrossum, serhiy.storchaka _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue25864> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
