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Generic default type in type revealed as Any #21608
Description
Bug Report
mypy reveals a certain nested default generic type in type as Any, while other type checkers reveal it as the default type.
This issue is motivated by pandas-dev/pandas-stubs#1764.
To Reproduce
This is complicated, see #21608 (comment) for a much simplified example.
from typing import Any, Generic, TypeVar, reveal_type
_ItemT_co = TypeVar("_ItemT_co", default=Any, covariant=True)
class generic(Generic[_ItemT_co]): ...
_ScalarT_co = TypeVar("_ScalarT_co", bound=generic, default=Any, covariant=True)
class dtype(Generic[_ScalarT_co]): ...
_DT64ItemT_co = TypeVar(
"_DT64ItemT_co", bound=int | None, default=int | None, covariant=True
)
class datetime64(generic[_DT64ItemT_co], Generic[_DT64ItemT_co]): ...
GenericT_co = TypeVar("GenericT_co", bound=generic, default=Any, covariant=True)
GenericT = TypeVar("GenericT", bound=generic, default=Any)
class Series(Generic[GenericT_co]):
def to_numpy_simplified(
self, dtype: dtype[GenericT] | type[GenericT]
) -> GenericT: ...
reveal_type(Series().to_numpy_simplified(datetime64)) # mypy: datetime64[Any], pyright & pyright: datetime64[int | None]- https://gist.github.com/mypy-play/099705d9f12556f66776949caa6f0450
- https://pyright-play.net/?strict=true&code=GYJw9gtgBALgngBwJYDsDmUkQWEMoCCKcANFAOICmKlISAxmQCqKUBqAhiGSJQG6UOAGwD68BJQCwAKBkiAkjEoQmI%2BmCgBeKCwmcQACgBECpSrVgjZACaVgHAK5CYmoqSjq%2BXJBxQumIA6UAJQyMvRCHADOUVBo1LQMBlQ0dPQA2qbKquoAusEAXFAAdKVh0iIAyvTCXDka2rrsXMZVNZEg9VZQAEZgDijWmvGpDDZ2js6uxGSe3r7%2BgSHlEdGx1uKUyQlpmdW1nRb5RaXF5SIAIkwAbAAsitkWWjqs%2BgYyUJ9QJld3D%2Bbqbp9AZDVD4AA%2BUAAcmAaON7E4XGCoJCYXCPGAvHQFpoAkEZKFZNJVjEoNYOEoYFhKHcDCNEhlLjd7mZ6rkyCkGZlfizHnlCiUykTOWl6s8mm8jCKGF0yMDBsMdmMyRNEdN3HNsX5cUtCdL6Exxa8WlKlQagf0FfS0vDJi43ITwpFSZVEpQottRhl9WzCh8vrZgLAwCIUA5sHARFEsAghEhgEhKNZ3tIvmmoFFKEJgDZNkUNqx0j7cijYIXi-7PsEoABaAB8FDNTBOQpkvAEwjErAMrro7oMwWKMBDYYjUZjcYTSYM5Mp1LuwUJQA
- https://play.ty.dev/8c070d59-a962-4cd0-823f-fa8dd9941f4f
Expected Behavior
datetime64[int | None]
Actual Behavior
datetime64[Any]
Activity
JelleZijlstra commentedon Jun 12, 2026
Simpler repro case:
fix: python/mypy#21608
[-]Nested generic default type revealed as `Any`[/-][+]Generic default type in `type` revealed as `Any`[/+]BUG: 🌃 `mypy` nightly (#1764)
ilevkivskyi commentedon Jun 14, 2026
Isn't this a duplicate of #20354?
That said, it is not obvious that the current behavior is wrong.
BUG: 🌃 `mypy` nightly (pandas-dev#1764)