After I generate an UML diagram from collections.abc, I found very strange that MappingView inherit from Sized instead of Collection (new in python 3.6).Yes, MappingView only define __len__ and not __iter__ and __contains__, but all of its subclasses define them (KeysView, ValuesView and ItemViews).I tried to run the tests in test/test_collections.py after making this change and on only one fail :Traceback (most recent call last):File "/usr/lib/python3.6/test/test_collections.py", line 789, in test_Collection self.assertNotIsInstance(x, Collection)AssertionError: dict_values([]) is an instance of <class 'collections.abc.Collection'>Wich is absolutely wrong, since in reality a dict_values instance has the behaviour of a Collection:>>> vals = {1:'a', 2: 'b'}.values()>>> 'a' in valsTrue>>> 'c' in valsFalse>>> len(vals)2>>> for val in vals:... print(val)...abThe only lack is that it doesn't define a __contains__ method:>>> '__contains__' in valsFalseIt uses __iter__ to find the presence of the value.But, hey: we have register() for this cases! In fact, when MappingView inherit from Collection, dict_values is considered as a subclass of Collection since it's in the register of ValuesView, causing the above bug...So, the test have to be changed, and dict_values must be placed in the samples that pass the test, and not in the ones that fail it.Maybe we can open an issue on the python bug tracker?
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