signature keeping wrapt decorator typing

[andythomas]

I did my best to type a wrapt decorator in a way that the original signature of the decorated function is still visible, but I was not able to do it. Some error always occurred. To my understanding, this is caused by:

@wrapt.decorator
def pass_through(wrapped, instance, args, kwargs):
    return wrapped(*args, **kwargs)

instead of

@wrapt.decorator
def pass_through(wrapped, instance, *args, **kwargs):
    return wrapped(*args, **kwargs)

According to ParamSpec and PEP612 the correct type information is

def with_request(f: Callable[Concatenate[Request, P], R]) -> Callable[P, R]:
  def inner(*args: P.args, **kwargs: P.kwargs) -> R:
    return f(Request(), *args, **kwargs)
  return inner

as an example. However, args: P.args raises an error. Does anyone have an idea/solution to this?

EDIT: Use better?! example.

[GrahamDumpleton]

The decorator wrapper function is not meant to use * or **. See example in docs at:

• https://wrapt.readthedocs.io/en/master/typing.html

of what you are meant to use.

After fixing how you declare the decorator and type hints per the documentation if you still have issues post the full example along with how you define P, R etc.

[andythomas]

Thank you for the quick reply. I tried to follow the example closely and get:

from collections.abc import Callable
from typing import Any, ParamSpec, TypeVar

import wrapt

P = ParamSpec("P")
R = TypeVar("R")


@wrapt.decorator
def pass_through(
    wrapped: Callable[P, R],
    instance: Any,
    args: tuple[Any, ...],
    kwargs: dict[str, Any],
) -> R:
    return wrapped(*args, **kwargs)


@pass_through
def function():
    pass

and I get

ERROR Expected *-unpacked P.args and **-unpacked P.kwargs [invalid-param-spec]
  --> wraptError.py:17:19
   |
17 |     return wrapped(*args, **kwargs)
   |                   ^^^^^^^^^^^^^^^^^
   |
 INFO 1 error

Any iteration I try get some error in at least one place.

EDIT: I use pyrefly.

[GrahamDumpleton]

I know nothing of pyrefly. Mypy has problems with some special case usage of type hints for wrapt as well, but pyright in VS code has for me so far worked okay. So some tools just seem to have problems with wrapt type hinting. I would suggest asking pyrefly developers. I know of nothing as yet to say what wrapt does is not allowed or wrong.

Note that I will be offline now for a few days so may not be able to response again quickly if provide an update.

[andythomas]

Thank you for the updates, I appreciate it! I will report back what the pyrefly people say. Enjoy the time offline :)

[andythomas]

Please see the comments in the linked issue. To my understanding

args or **kwargs [...] would be a more precise annotation compared to the tuple/dict.

facebook/pyrefly#1820 (comment), but I cannot say that I really understand these more complex typing details. However, they amended pyrefly to also allow the typing of your example. The PR comment says:

This allows tuple[Any, ...] to be used where P.args is expected, and dict[str, Any] to be used where P.kwargs is expected. I check against Never s.t. only Any will match.

I'm not 100% sure about the dict case, but I think it makes sense to extend these gradual types to param spec handling.

facebook/pyrefly@5fefb00

I will test the newest version and close.