Alexey Izbyshev <izbys...@ispras.ru> added the comment: > Isn't it just a limitation? > Most Python-implemented objects supports weakref. I don't think "requiring > weakref support implies it must be type object".
Formally, there is no implication. It is the abc module authors who know the truth. But I can't imagine why anybody would impose such a limitation by design, because while instances of user-defined classes support weakrefs, built-in classes used by everybody like tuple, list and dict don't. That's why I guessed that non-types were not meant to be supported. > What "by OP" means? OP = Original poster (@jab). > I can't find `if not issubclass(cls, type): raise TypeError` in Reversible > implementation. > They do duck-typing, same to ABC. Sorry for being unclear. There is no explicit check as you say, but __mro__ is directly accessed (see msg313376). But it may probably be considered "duck typing" too. > But I don't know much about how mages use ABC. I need mages comment before > merging the pull request. Totally agree. > BTW, do you think it should be backported to 3.7, or even 3.6? 3.7 certainly has my vote -- this can hardly be considered a new feature. For 3.6, I'd listen to ABC users/experts. Might raising a TypeError instead of returning False from issubclass(user_defined_obj, ABC) break something important? Personally, I think it would mostly expose bugs and not hinder reasonable usage. > Can > https://github.com/python/cpython/commit/fc7df0e664198cb05cafd972f190a18ca422989c > be reverted? Seems like it can, but the test should survive in some form :) ---------- _______________________________________ 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
