  
      def to_native(self, value):
          if isinstance(value, datetime.datetime):
              value = value.time()
          if self.output_format.lower() == ISO8601:
              return value.isoformat()
          return value.strftime(self.output_format)
  
  
  class IntegerField(WritableField):
 
</s> remove         return value.strftime(self.output_format)
 </s> add         return value.strftime(self.format) </s> remove         if self.output_format.lower() == ISO8601:
 </s> add         if self.format.lower() == ISO_8601: </s> remove         return value.strftime(self.output_format)
 </s> add         return value.strftime(self.format) </s> remove         return value.strftime(self.output_format)
 </s> add         return value.strftime(self.format) </s> remove         if self.output_format.lower() == ISO8601:
 </s> add         if self.format.lower() == ISO_8601:
        if self.format.lower() == ISO_8601:
  
      def to_native(self, value):
          if isinstance(value, datetime.datetime):
              value = value.time()
        if self.format.lower() == ISO_8601:
              return value.isoformat()
          return value.strftime(self.output_format)
  
  
  class IntegerField(WritableField):
keep keep keep keep replace keep keep keep keep keep
 Clean ups to datetime formatting 
rest_framework/fields.py