Can you annotate return type when value is instance of cls?

Question

Given a class with a helper method for initialization:

class TrivialClass:
    def __init__(self, str_arg: str):
        self.string_attribute = str_arg

            


        

Answer 1

From Python 3.7 you can use __future__.annotations:

from __future__ import annotations


class TrivialClass:
    # ...

    @classmethod
    def from_int(cls, int_arg: int) -> TrivialClass:
        # ...
        return cls(...)

Edit: you can't subclass TrivialClass without overriding the classmethod, but if you don't require this then I think it's neater than a forward reference.