How to Resolve Cyclic Import Issues and Utilize Type Hints in Python Class Split?

Type Hinting in Python without Cyclic Imports

Type hints in Python offer valuable assistance in code completion and static type checking. However, issues arise when attempting to split a class into multiple files while maintaining type hints due to cyclic imports.

One approach to resolve this issue is to introduce an abstract base class (ABC) as an intermediary. This requires modifying both the main class and the mixin file:

main.py:

<code class="python">from abc import ABC
from mymixin import MyMixinABC

class Main(MyMixinABC):
    def func1(self, xxx):
        ...</code>

mymixin.py:

<code class="python">import abc

class MyMixinABC(abc.ABC):
    def func2(self: 'MyMixinABC', xxx):
        ...</code>

By using an ABC, we establish a formal contract between the main class and the mixin. Type hints can now accurately refer to the ABC instead of the actual class name.

For Python 3.7 users, a more concise approach is possible using PEP 563:

main.py:

<code class="python">from __future__ import annotations

class Main:
    def func1(self, xxx):
        ...</code>

mymixin.py:

<code class="python">from __future__ import annotations

class MyMixin:
    def func2(self, xxx):
        ...</code>

These techniques allow you to split your class into multiple files while preventing cyclic imports and preserving the benefits of type hinting in your code.

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