Documentation

Calling defaultdict(default_factory=list) (as suggested by the docs) does not create a defaultdict where the default factory is list. Instead, it creates a defaultdict where the default_factory is None and elements {"default_factory": list}.

https://docs.python.org/3/library/collections.html#collections.defaultdict

Linked PRs

• gh-131490: Clarify defaultdict keyword argument behavior in docs #131491