dict() should support anything with .keys() and __getitem__

[Akuli]

from typing import List
class Foo:
    def keys(self) -> List[str]:
        return ['a', 'b', 'c']
    def __getitem__(self, key: str) -> str:
        return f'value of {key}'
print(dict(Foo()))   # {'a': 'value of a', 'b': 'value of b', 'c': 'value of c'}

works at runtime but fails type check

tkinter widgets are like this, they aren't Mapping but they have .keys() and __getitem__

[srittau]

Sounds reasonable. See also #3576 and #4325.