Could you explain what a Protocol is in the typing module in Python?

Protocol in Python's typing module is a way to describe an interface (a set of methods and attributes) that an object must support, without needing to inherit from a specific class.

It is part of the concept of "structural typing," where what matters is not the object's belonging to a particular class, but the presence of the required methods and properties.

Example of using Protocol:

from typing import Protocol

class SupportsClose(Protocol):
    def close(self) -> None:
        ...

class Resource:
    def close(self) -> None:
        print("Closed")


def cleanup(resource: SupportsClose) -> None:
    resource.close()

r = Resource()
cleanup(r)  # Works because Resource has a close method

Thus, Protocol allows describing requirements for objects for static type checking without forcing them to explicitly inherit from any base class.