MutableMapping.setdefault() is buggy, needs overload for one-argument case

[Akuli]

I think https://github.com/python/typeshed/blob/61d876e4ea62c42599dbaa59471576d6eda0e04d/stdlib/typing.pyi#L480 is buggy. It needs an overload for the case where the second argument is not specified.

Originally posted by @JelleZijlstra in #1033 (reply in thread)

(Edit by Akuli: link to a specific commit instead of master)

[JelleZijlstra]

This is a typeshed issue. I opened python/typeshed#6941 to address it.

[Akuli]

Lol, I forgot that the discussions aren't in typeshed :)