Andrew Barnert added the comment: > I did actually mean a version changed notice for the data model change. I see > this as a small expansion of the Python object API. Previously, > __reversed__() had to be a function, now you are also allowed to set it to > None. The collections ABCs are just catching up with the API change.
Are you suggesting that in Python 3.5, it's not defined what happens if you set __reversed__ = None on a sequence-like object and then call reversed()? I think any implementation has to raise a TypeError; the only difference is that we're now documenting the behavior directly, rather than forcing you to infer it from reading a half-dozen different parts of the docs and tracing through the implied behavior. It's already the best way to do it in 3.5, or even 2.5; the problem is that it isn't _obviously_ the best way. And I think a version-changed would send the wrong message: someone might think, "Oh, I can't use None here because I can't require 3.6, so what should I do? Write a method that raises TypeError when called?" (Which will work, but will then make it very hard to write a Reversible implicit ABC if they later want to.) > Imagine someone using an Orderable virtual base class that tested for > __gt__() etc. That's part of what we're trying to solve. Do you test that with hasattr, like Sized, or do you test for getattr with default None, like Hashable? ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue25958> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
