Python/Django typing and circular dependencies

mixins.py

from module.models import MainThing

class ActivityMixin:
  is_active = models.BooleanField(default=False)

  def activate(self: MainThing):
    # Type definition up there would help PyCharm and other editors
    # to know that they could access the method of the main class,
    # BUT it requires an import of the model, which leads to a circular import issue.
    # How can we solve it?
    title = self.get_current_title_for_no_reason()
    self.is_active = True
    self.save(update_fields=['is_active'])

models.py

from django.db import models

class MainThing(ActivityMixin, models.Model):
  """My very big and complex model, in which I decided to separate some logic into a mixins.py file""""
  title = models.CharField(max_length=100)

  def get_current_title_for_no_reason(self):
    return self.title