=== This proposition is purely aesthetic ===
At this time, the __repr__ of the mapping views is showing the whole mapping:
>>> from collections.abc import ValuesView, KeysView, ItemsView
>>> d = {3: 'three', 4: 'four'}
>>> KeysView(d)
KeysView({3: 'three', 4: 'four'})
>>> ValuesView(d)
ValuesView({3: 'three', 4: 'four'})
>>> ItemsView(d)
ItemsView({3: 'three', 4: 'four'})
Witch is not consistent with dict_keys, dict_values, dict_items:
>>> d.keys()
dict_keys([3, 4])
>>> d.values()
dict_values(['three', 'four'])
>>> d.items()
dict_items([(3, 'three'), (4, 'four')])
We could easily change that, since all the views are iterables on what they are
designed for, in MappingView:
def __repr__(self):
viewname = self.__class__.__name__
elements = ', '.join(map(repr, self))
return f'{viewname}([elements])
And now:
>>> KeysView(d)
KeysView([3, 4])
>>> ValuesView(d)
ValuesView(['three', 'four'])
>>> ItemsView(d)
ItemsView([(3, 'three'), (4, 'four')])
It's not breaking any test (it seems that there isn't any for this), but it
have a real drawback: it's breaking the convention about instantiation by
copy/pasting:
>>> ValuesView(['three', 'four'])
Traceback (most recent call last):
File "/usr/lib/python3.6/site-packages/IPython/core/formatters.py", line 684,
in __call__
return repr(obj)
File "/usr/lib/python3.6/_collections_abc.py", line 706, in __repr__
elements = ', '.join(map(repr, self))
File "/usr/lib/python3.6/_collections_abc.py", line 764, in __iter__
yield self._mapping[key]
TypeError: list indices must be integers or slices, not str
It's because __init__ in MappingView treat the passed argument -- wich is
stored in self._mapping -- as the whole mapping, not just keys, values or
items... And all the other methods (__contains__ and __iter__) in the
subclasses are using this _mapping attribute to work.
So what is to prioritize?
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