type hint for generic attribute inside abstract class

Question

I have a convoluted problem with types that I can´t solve.

Let’s say I have some abstract classes and a generic type equivalent to this

from abc import ABC
from typing import Generic, TypeVar


class Action(ABC):
    pass

ActionTypeVar = TypeVar("ActionTypeVar", bound="Action")

class Agent(ABC, Generic[ActionTypeVar]):
    actions: tuple[ActionTypeVar, ...]

    def get_action() -> ActionTypeVar:
       return self.action[0]

This works as intended. But I need is to define a function similar to get_action outside the class(in a different package in fact).

def get_action_outside_class(agent: Agent) -> ActionTypeVar:
    return agent.actions[0]

The problem is that here the return type is not precise anymore, since we are outside the scope of the class. I wanted to indicate this is of the same type as the elements of agent.actions.

I have tried referencing the elements of Agent.actions in the return of get_action but I can’t find out a proper way to do it.

Asked By: hmnoir

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Source

Answer 1

You aren’t using Agent generically.

def get_action_outside_class(agent: Agent[ActionTypeVar]) -> ActionTypeVar:
    return agent.actions[0]

(Any TypeVar would do; it doesn’t need to be the same one you used when defining Agent.)

Answered By: chepner

type hint for generic attribute inside abstract class

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