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Tuple types don't work with higher level typing
mypy 1.8.0, python 3.10.10
So tuple types get matched and checked normally in simple situations like this:
a: tuple[int, int] = (2, "a")
# Incompatible types in assignment ...
But imagine I want to define a function that takes a type and returns a value of that type (e.g. by deserializing something as the given type):
from typing import Tuple, TypeVar, Type, List
_T = TypeVar("_T")
def structure(structure_into: Type[_T], obj: str) -> _T:
raise NotImplementedError
This works with builtin types, or with generics like List:
reveal_type(structure(int, "a"))
# Revealed type is "builtins.int"
reveal_type(structure(List[int], "a"))
# Revealed type is "builtins.list[builtins.int]"
... but not with tuples:
reveal_type(structure(Tuple[int, int], "a"))
# note: Revealed type is "Never"
# error: Argument 1 to "structure" has incompatible type "object"; expected "type[Never]" [arg-type]
Trying to reveal the type of Tuple itself leads to strange results too (compared to List[...]):
reveal_type(Tuple[int, int])
# Revealed type is "builtins.object"
reveal_type(tuple[int, int])
# Revealed type is "def [_T_co] (typing.Iterable[_T_co`1] =) -> builtins.tuple[_T_co`1, ...]"
So the question is, why does Tuple get a special treatment, and is there a way to make it behave like other generics?
