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pythonpython-3.xtype-hinting

Python: TypeVar for multiple arguments at once

Is there a way to have a TypeVar (or some other format) capture all the arguments of a function? For example, say I want to wrap a general function, such that all its arguments are given within a tuple:

def invoke(f: Callable[..., T], args: Tuple[...]) -> T:
    return f(*args)

Only that instead of the ellipsis (...), I'll have the static-type inspection enforce the contents of the Tuple to be have the same types as the function's arguments.

Thanks.

Solution

  • The answer is Yes, just not with TypeVar. One should use ParamSpec:

    from typing import ParamSpec, TypeVar, Callable
P = ParamSpec('P')
RT = TypeVar('RT')

def invoke(f: Callable[P, RT], args: P.args) -> RT:
    return f(*args)

# Or, makes more sense:

def invoke(f: Callable[P, RT], args: P.args, **kwargs: P.kwargs) -> RT:
    return f(*args, **kwargs)

    Note that for python < 3.10, one should import it from typing_extensions rather than typing.