Originally posted by @AlexWaygood in #106354 (comment):

Tools/clinic/clinic.py:5039: error: Incompatible return value type (got
"tuple[str, bool, dict[str | None, Any]]", expected
"tuple[str, bool, dict[str, Any]]")  [return-value]
                    return name, False, kwargs
                           ^~~~~~~~~~~~~~~~~~~

I think mypy is flagging a real bug in the code here. The issue is this block of code here:

The function is annotated as return tuple[str, bool, KwargDict], and KwargDict is a type alias for dict[str, Any]. It's important that the dictionary that's the third element of the tuple only has strings as keys. If it doesn't, then this will fail:

The code as written, however, doesn't guarantee that all the keys in the kwargs dictionary will be strings. In the dictionary comprehension, we can see that annotation is an ast.Call instance. That means that annotation.keywords is of type list[ast.keyword] -- we can see this from typeshed's stubs for the ast module (which are an invaluable reference if you're working with ASTs in Python!): https://github.com/python/typeshed/blob/18d45d62aabe68fce78965c4920cbdeddb4b54db/stdlib/_ast.pyi#L324-L329. If annotation.keywords is of type list[ast.keyword], that means that the node variable in the dictionary comprehension is of type keyword, which means (again using typeshed's ast stubs), that node.arg is of type str | None: https://github.com/python/typeshed/blob/18d45d62aabe68fce78965c4920cbdeddb4b54db/stdlib/_ast.pyi#L516-L520. AKA, the keys in this dictionary are not always guaranteed to be strings -- there's a latent bug in this code!

Linked PRs

• gh-106359: Fix corner case bugs in Argument Clinic converter parser #106361
• [3.12] gh-106359: Fix corner case bugs in Argument Clinic converter parser (GH-106361) #106364