code: def _validate_overriden_fields_are_not_defined_in_superclasses(class_to_field_type_overrides,
                                                                 schema_graph):
      
      for class_name, field_type_overrides in six.iteritems(class_to_field_type_overrides):
          for superclass_name in schema_graph.get_inheritance_set(class_name):
              if superclass_name != class_name:
                  superclass = schema_graph.get_element_by_class_name(superclass_name)
                  for field_name in field_type_overrides:
                      if field_name in superclass.properties:
                          raise AssertionError(
                              u'Attempting to override field "{}" from class "{}", but the field is '
                              u'defined in superclass "{}"'
                              .format(field_name, class_name, superclass_name))
docs: Assert that the fields we want to override are not defined in superclasses.