[FIXED] Python: Protocol requiring class property

Issue

My method requires an object with the attribute pattern and the function handle. To this end, I wrote a Protocol instance with these two members. Consider the following code:

class Handler(typing.Protocol):
    """Handler protocol"""

    pattern: re.Pattern

    @staticmethod
    def handle(match: re.Match) -> str:
        pass


def f(obj: Handler, text: str):
    output = []
    for match in re.finditer(obj.pattern, text):
        output.append(obj.handle(match))
    return output


class MyHandler(Handler):
    pattern = re.compile("hello world")

    @staticmethod
    def handle(match: re.Match) -> str:
        return "hi there"


f(MyHandler, 'hello world, what a nice morning!')

However, when I call this function with MyHandler, my IDE (PyCharm) issues the following warning:

Expected type 'ReplacerProtocol', got 'Type[CitationReplacer]' instead

This warning goes away when I remove the pattern attribute from the protocol class. When I change the protocol to require a @property or a function with the name pattern, the same warning is issued.

What is the correct way to define my interface in Python?

Solution

As per suggested by Sterliakov, I made edits to my code. I removed the use of @property in the implementation of MyHandler as it was deemed unnecessary for the protocol. Additionally, I incorporated generics (re.Pattern[str] and re.Match[str]) as advised.

import typing

class Handler(typing.Protocol):
    """Handler protocol"""

    pattern: re.Pattern[str]

    @staticmethod
    def handle(match: re.Match[str]) -> str:
        ...


def f(obj: Handler, text: str) -> list[str]:
    output = []
    for match in re.finditer(obj.pattern, text):
        output.append(obj.handle(match))
    return output


class MyHandler:
    pattern: re.Pattern[str] = re.compile("hello world")

    @staticmethod
    def handle(match: re.Match[str]) -> str:
        return "hi there"


result = f(MyHandler(), 'hello world, what a nice morning!')
print(result)

Answered By - Umar