  
      _options_class = SerializerOptions
      _dict_class = SortedDictWithMetadata  # Set to unsorted dict for backwards compatibility with unsorted implementations.
  
      def __init__(self, instance=None, data=None, files=None, context=None, partial=False, **kwargs):
          super(BaseSerializer, self).__init__(**kwargs)
          self.opts = self._options_class(self.Meta)
          self.parent = None
          self.root = None
          self.partial = partial
 
</s> remove             # Set up the field
            field.initialize(parent=self, field_name=key)
 </s> add  </s> remove     ManyToManyModel, Person, ReadOnlyManyToManyModel)
 </s> add     ManyToManyModel, Person, ReadOnlyManyToManyModel, Photo)
    def __init__(self, instance=None, data=None, files=None,
                 context=None, partial=False, **kwargs):
  
      _options_class = SerializerOptions
      _dict_class = SortedDictWithMetadata  # Set to unsorted dict for backwards compatibility with unsorted implementations.
  
    def __init__(self, instance=None, data=None, files=None,
                 context=None, partial=False, **kwargs):
          super(BaseSerializer, self).__init__(**kwargs)
          self.opts = self._options_class(self.Meta)
          self.parent = None
          self.root = None
          self.partial = partial
keep keep keep keep replace keep keep keep keep keep
 Clean up field initialization.  Fixes #497 
rest_framework/serializers.py