New submission from Serhiy Storchaka: collections.abc.Reversible doesn't work with types that are supported by reserved() but neither have the __reversed__ method nor are explicitly registered as collections.abc.Sequence. For example:
>>> issubclass(array.array, collections.abc.Reversible) False The reversing protocol as well as the iterating protocol is supported not only by special method, but implicitly if the class has implemented __getitem__ and __len__ methods. >>> 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, collections.abc.Reversible) False typing.Reversible starves from the same bug. See https://github.com/python/typing/issues/170. ---------- components: Library (Lib) messages: 289039 nosy: gvanrossum, rhettinger, serhiy.storchaka, stutzbach priority: normal severity: normal status: open title: collections.abc.Reversible doesn't fully support the reversing protocol type: behavior versions: Python 3.6, Python 3.7 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue29727> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
