Yahya Abou Imran <yahya-abou-im...@protonmail.com> added the comment:
Quoting my own post on python-ideas:
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.
Here is a patch file for this.
The only problem in this is that the MappingView won't be instatiable anymore
because of the lack of __contains__ and __iter__.
But since - if my understanding is correct - it's just an "utilty" super class
for three other views (so is Collection for Set, Mapping and Sequence), it's
not a big deal IMHO.
----------
keywords: +patch
Added file: https://bugs.python.org/file47354/mypatch.patch
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<https://bugs.python.org/issue32449>
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