How could a python class call a class method which was not defined or inherited?

Question

I'm reading the source code of mixin.py from rest_framework, here is the link to GitHub.

Let's take the CreateModelMixin class as an example, here is the code:

from rest_framework import status
from rest_framework.response import Response
from rest_framework.settings import api_settings


class CreateModelMixin:
    """
    Create a model instance.
    """
    def create(self, request, *args, **kwargs):
        serializer = self.get_serializer(data=request.data)
        serializer.is_valid(raise_exception=True)
        self.perform_create(serializer)
        headers = self.get_success_headers(serializer.data)
        return Response(serializer.data, status=status.HTTP_201_CREATED, headers=headers)

    def perform_create(self, serializer):
        serializer.save()

    def get_success_headers(self, data):
        try:
            return {'Location': str(data[api_settings.URL_FIELD_NAME])}
        except (TypeError, KeyError):
            return {}

I can understand the lines self.perform_create() and self.get_success_headers() because they are class methods defined within the class. But how did the line self.get_serializer(data=request.data) work?

My understandings so far:

• The class CreateModelMixin did not inherit any classes
• get_serializer() was not imported from other files
• get_serializer() was not defined with class