Alexey Izbyshev <izbys...@ispras.ru> added the comment: I do not see any point in allowing non-types in ABCMeta.__subclasscheck__. Currently, ABCs are clearly not designed to support non-types:
1. ABCMeta.register() accepts types only. 2. ABCMeta.__subclasscheck__ implicitly requires its arguments to support weak references (regardless of whether __subclasshook__ is called or not). This requirement alone doesn't make sense, so it seems to be an exposed implementation detail stemming from the fact that non-types were not intended to be supported. 3. Some ABC users already expect that the argument of __subclasshook__ is a type (see the example with collections.abc.Reversible by OP). 4. Attempting to support arbitrary arguments in ABC.__subclasscheck__ (by returning False instead of raising TypeError or worse) will not solve any 'issubclass' inconsistencies. 'issubclass' is fundamentally "fragmented": issubclass(x, y) may return True/False while issubclass(x, z) may raise TypeError, depending on __subclasscheck__ implementation. It may be too late to impose stricter requirements for the first argument of issubclass because 'typing' module relies on the support of non-types there. ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue33018> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
