New submission from Geoffrey Sneddon <geoffers+pythonbugs@gmail.com>: The mixin methods on MappingView and its subclasses all rely on the undocumented MappingView._mapping (set in the undocumented MappingView.__init__). This should probably be documented at least insofar as Set._from_iterable is. ---------- assignee: docs@python components: Documentation messages: 344447 nosy: docs@python, gsnedders priority: normal severity: normal status: open title: collections.abc.MappingView mixins rely on undocumented _mapping type: behavior versions: Python 2.7, Python 3.5, Python 3.6, Python 3.7, Python 3.8, Python 3.9 _______________________________________ Python tracker <report@bugs.python.org> <https://bugs.python.org/issue37145> _______________________________________