[docs] [issue37145] collections.abc.MappingView mixins rely on undocumented _mapping

Raymond Hettinger <raymond.hettinger@gmail.com> added the comment:

Then I guess what I consider a bug is "__init__ is undocumented".

No, this just how Python works. ---------- _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue37145> _______________________________________