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type-hintingpython-3.9
mikb
mikb

Reputation: 315

Question about type hinting in Python 3.9+

I have a method that takes a callback function as an argument.

I want to specify a type hint for the callback function signature.

The problem is the signature of the callback function is:

def callback_function(event, token, *args)

where

type(event) = EventClass
type(token) = str
type(args) = tuple  # of str

I could write this as:

callable[[...], returntype]

but I would like to tighten the type checking to be something useful, at least to making sure event and token are specified correctly.

Suggestions, please?

Upvotes: 0

Views: 390

Answers (1)

Adam Bright
Adam Bright

Reputation: 166

Consider using Protocol for this matter, as answered before.

For your specific case it will look like this:

from typing import Protocol, TypeAlias

returntype: TypeAlias = int

class MyCallable(Protocol):
    def __call__(self, event: EventClass, token: str, *args: str) -> returntype: ...


def some_function(callback: MyCallable): ...

Upvotes: 1

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