mypy doesn't understand dict contstruction

from typing import Any, Callable, List, Mapping, Tuple, TypeVar

U = TypeVar('U', bound=Mapping[str, Any])


def f(dict_factory: Callable[[List[Tuple[str, Any]]], U] = dict) -> U:
    return dict_factory([('a', 1)])

prints

main.py:6: error: Incompatible default for argument "dict_factory" (default has type "Type[Dict[Any, Any]]", argument has type "Callable[[List[Tuple[Any, Any]]], U]")

This is from trying to annotate dataclasses.asdict.

Start with the provided example in main.py and reproduce the incompatible-default error. Then trace mypy’s handling of the dict default against the TypeVar-bound Mapping signature and compare it with the dataclasses.asdict annotation goal. Done means the example type-checks without that error while preserving the intended return type.