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 vals True 'c' in vals False len(vals) 2 for val in vals: ... print(val) ... a b
The only lack is that it doesn't define a __contains__ method:
'__contains__' in vals False
It 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?