[Python] Correct annotation for "apply" function

In Python-3.10 (it must be this version) I want to add better annotation for my apply function:

from typing import TypeVar, Callable, Sequence, Any

T = TypeVar('T')

def apply(fn: Callable[..., T], vals: Sequence[Any]) -> T:
return fn(*vals)

def f(a: int, b: int) -> int:
return a + b

print(apply(f, (1, 2)))


Because in this code, the type annotation "hides" the connection between vals and fn arguments, so mypy can't check types and number of arguments correctly.

What have I tried:

1. using ParamSpec


from typing import ParamSpec

P = ParamSpec('P')

def apply(fn: Callable[P, T], vals: P) -> T:
return fn(*vals)


which gives this error:

tst_apply.py:6: error: Invalid location for ParamSpec "P" [valid-type]
tst_apply.py:6: note: You can use ParamSpec as the first argument to Callable, e.g., "Callable[P, int]"
tst_apply.py:7: error: Too few arguments [call-arg]
Found 2 errors in 1 file (checked 1 source file)

2. using ParamSpec.args


from typing import ParamSpec

P = ParamSpec('P')

def apply(fn: Callable[P, T], vals: P.args) -> T:
return fn(*vals)


which gives this error:

tst_apply.py:7: error: Too few arguments [call-arg]
Found 1 error in 1 file (checked 1 source file)

3. using TypeVarTuple as suggested in Daraan's answer Revision 1:


Even though TypeVarTuple is available only from python-3.11, I can import it from typing_extensions, but it still doesn't work - it works when I change vals: *Ts to *vals: *Ts but that's unusable for me:

Ts = TypeVarTuple('Ts')

def apply(fn: Callable[[*Ts], T], vals: *Ts) -> T:
return fn(*vals)


which gives this error:

tst_apply.py:7: error: invalid syntax [syntax]
def apply(fn: Callable[[*Ts], T], vals: *Ts) -> T:
^
Found 1 error in 1 file (errors prevented further checking)

4. using Tuple[*Ts] for TypeVarTuple:


def apply(fn: Callable[[*Ts], T], vals: Tuple[*Ts]) -> T:
return fn(*vals)


which gives this error:

tst_apply.py:7: error: invalid syntax. Perhaps you forgot a comma? [syntax]
def apply(fn: Callable[[*Ts], T], vals: Tuple[*Ts]) -> T:
^
Found 1 error in 1 file (errors prevented further checking)

Question:


Is there a way to annotate this so the connection between fn parameters and vals is not lost?

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