Maybe it's intended to be like that, but if some class implements all the necessary methods for KeysView, ValuesView or ItemsView, mypy will generate errors, although python code will work:
from collections.abc import ItemsView, KeysView, ValuesView
from typing import Iterator
class Map[KT, VT]:
def __init__(self, mapping: dict[KT, VT]) -> None:
self._items: dict[KT, VT] = mapping
def __getitem__(self, key: KT) -> VT:
return self._items[key]
def __len__(self) -> int:
return len(self._items)
def __iter__(self) -> Iterator[KT]:
return iter(self._items)
a = Map[int, int]({3: 4})
keys = KeysView(a)
values = ValuesView(a)
items = ItemsView(a)
print(list(keys))
print(len(keys))$ mypy t.py
t.py:20: error: Need type annotation for "keys" [var-annotated]
t.py:20: error: Argument 1 to "KeysView" has incompatible type "Map[int, int]"; expected "Mapping[Never, Any]" [arg-type]
t.py:21: error: Need type annotation for "values" [var-annotated]
t.py:21: error: Argument 1 to "ValuesView" has incompatible type "Map[int, int]"; expected "Mapping[Any, Never]" [arg-type]
t.py:22: error: Need type annotation for "items" [var-annotated]
t.py:22: error: Argument 1 to "ItemsView" has incompatible type "Map[int, int]"; expected "Mapping[Never, Never]" [arg-type]
Found 6 errors in 1 file (checked 1 source file)
In my case I couldn't add multiple inheritance with Mapping because of metaclass conflict
Maybe it's intended to be like that, but if some class implements all the necessary methods for
KeysView,ValuesVieworItemsView,mypywill generate errors, althoughpythoncode will work:In my case I couldn't add multiple inheritance with
Mappingbecause of metaclass conflict