  class SerializerMetaclass(type):
      """
      This metaclass sets a dictionary named `base_fields` on the class.
  
      Any fields included as attributes on either the class or it's superclasses
      will be include in the `base_fields` dictionary.
      """
  
      @classmethod
      def _get_fields(cls, bases, attrs):
          fields = [(field_name, attrs.pop(field_name))
 
</s> remove     def get_default_fields(self):
        fields = super(HyperlinkedModelSerializer, self).get_default_fields()

        if self.opts.view_name is None:
            self.opts.view_name = self.get_default_view_name(self.opts.model)

        url_field_name = api_settings.URL_FIELD_NAME
        if url_field_name not in fields:
            ret = fields.__class__()
            ret[url_field_name] = self.get_url_field()
            ret.update(fields)
            fields = ret

        return fields

    def get_pk_field(self, model_field):
        if self.opts.fields and model_field.name in self.opts.fields:
            return self.get_field(model_field)

 </s> add 
    Any instances of `Field` included as attributes on either the class
    or on any of its superclasses will be include in the
    `base_fields` dictionary.
  class SerializerMetaclass(type):
      """
      This metaclass sets a dictionary named `base_fields` on the class.
  
    Any instances of `Field` included as attributes on either the class
    or on any of its superclasses will be include in the
    `base_fields` dictionary.
    Any instances of `Field` included as attributes on either the class
    or on any of its superclasses will be include in the
    `base_fields` dictionary.
      """
  
      @classmethod
      def _get_fields(cls, bases, attrs):
          fields = [(field_name, attrs.pop(field_name))
keep keep keep keep replace replace keep keep keep keep keep
 Added help_text argument to fields 
rest_framework/serializers.py