Is typing.Protocol with composition rather than inheritance even possible?

Users
#1

We are instructed to use inheritance with typing.Protocol. So like this…

import typing

class MyProtocolClass(typing.Protocol):
    ...

Is it possible to use composition instead? So like…

import typing

class MyProtocolClass:
    def __init__(self):
        self.my_protocol = typing.Protocol()

Am I completely misunderstanding the whole concept of Python’s typing.Protocol thing?

#2

What would that mean? It’s not meaningful to just instantiate Protocol.

#3

@Jelle, please elaborate on It’s not meaningful to just instantiate Protocol.

#4

Have you read PEP 544 which defines Protocol types? Or there is some more user-friendly explanation in the mypy docs.
To me, it’s not clear what you want to accomplish and how it might relate to Protocol.

#5

Protocol needs to be inherited to mark the child class as a protocol, and that’s also where you declare the signature of the child class. The Protocol class by itself doesn’t mean much at all.

2 Likes
#6

@EpicWink, thanks for this. Now I understand.