How Do I Type Hint a Method Using the Enclosing Class in Python?

How do I Type Hint a Method with the Type of the Enclosing Class?

Challenge:

In Python, when type hinting a method that expects an instance of the enclosing class as an argument and returns an instance of the same class, you may encounter error messages from your editor or code completion. This issue stems from the fact that the class may not be fully defined at the time of type hinting.

Solution:

To resolve this challenge, consider the following options:

Python 3.11 with from typing import Self

For Python versions 3.11 and later, use from typing import Self to annotate your method like so:

from typing import Self

class Position:
    def __add__(self, other: Self) -> Self:
        ...

Python 3.7 with from future import annotations

Enable the postponed evaluation of annotations by including from __future__ import annotations at the start of your module. This allows you to type hint using the class name:

from __future__ import annotations

class Position:
    def __add__(self, other: Position) -> Position:
        ...

Python < 3.7: Use a String

For Python versions below 3.7, use a string to represent the enclosing class in your type hints:

class Position:
    def __add__(self, other: 'Position') -> 'Position':
        ...
Limitations

While using a string may work with code completion, it's important to note that this approach is not fully supported by all Python versions and may lead to issues with static analysis tools.
Recommended Approach
For optimal results, it is recommended to use from typing import Self in Python 3.11  or from __future__ import annotations in Python 3.7  if available. This ensures that the type hinting is handled correctly and is compatible with the latest language features.
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