signal/slot patternmaking function signatures generic

[chadrik]

I'm trying to design a simple signal/slot package that is pep484-compatible, but it's proving trickier than I thought. The problem is that the type-checked signatures of the generic class's methods should vary depending on its parameterization.

Here's a naive rough draft:

# file: signal.py
from typing import Any, Callable, TypeVar, List

T = TypeVar('T')

class Signal(Callable[T, Any]):
    def __init__(self):
        self.slots: List[Callable[T, Any]] = []

    def connect(self, func: Callable[T, Any]):
        self.slots.append(func)

    def __call__(self, *args, **kwargs):
        "emit the signal"
        for slot in self.slots:
            slot(*args, **kwargs)

# file: signal.pyi
from typing import Any, Callable, TypeVar

T = TypeVar('T')

class Signal(Callable[T, Any]):
    def connect(self, func: Callable[T, Any]) -> None: ...

# file: main.py
from signal import Signal

IntStrSignal = Signal[[int, str]]
sig = IntStrSignal()

def cb(a: int, b: str):
    pass

sig.connect(cb)

sig(1, 'foo')

Any advice on the best way to proceed is greatly appreciated, esp. any low-hanging issues that could unlock this functionality.

Related to #4031

edit: removed emit method in favor of the callable's __call__ method

[chadrik]

It looks like I accidentally submitted this issue long before I was done editing, so if you got it by email you should click the link to the issue. Sorry!

[JelleZijlstra]

I don't know if this fixes your problem, but don't you want Callable[[T], Any] instead of Callable[T, Any]? The latter is invalid.

[chadrik]

I don't know if this fixes your problem, but don't you want Callable[[T], Any] instead of Callable[T, Any]? The latter is invalid.

Yes, it is invalid, but that's part of the problem in terms of expressive limitations. I don't want to limit Signal to callables with one argument. I want to capture the types of all of the args, and use that to restrict/overload the signatures of __call__ and connect. For example, in main.py I want T to hold [int, str], such that sig.connect fails for callables which don't match Callable[[int, str], Any]

[ilevkivskyi]

This is a duplicate of python/typing#264 (you can cast your vote in favour of special OtherArgs variadic type variable there, it is exactly what you want).