          humanized_format = humanize_datetime.datetime_formats(self.input_formats)
          self.fail('invalid', format=humanized_format)
  
      def to_representation(self, value):
          if self.format is None:
              return value
  
          if self.format.lower() == ISO_8601:
              value = value.isoformat()
              if value.endswith('+00:00'):
 
</s> remove         if self.format.lower() == ISO_8601:
 </s> add         if output_format.lower() == ISO_8601: </s> remove         humanized_format = humanize_datetime.datetime_formats(self.input_formats)
 </s> add         humanized_format = humanize_datetime.datetime_formats(input_formats) </s> remove         humanized_format = humanize_datetime.time_formats(self.input_formats)
 </s> add         humanized_format = humanize_datetime.time_formats(input_formats) </s> remove         humanized_format = humanize_datetime.date_formats(self.input_formats)
 </s> add         humanized_format = humanize_datetime.date_formats(input_formats)
        output_format = getattr(self, 'format', api_settings.DATETIME_FORMAT)

        if output_format is None:
          humanized_format = humanize_datetime.datetime_formats(self.input_formats)
          self.fail('invalid', format=humanized_format)
  
      def to_representation(self, value):
        output_format = getattr(self, 'format', api_settings.DATETIME_FORMAT)

        if output_format is None:
              return value
  
          if self.format.lower() == ISO_8601:
              value = value.isoformat()
              if value.endswith('+00:00'):
keep keep keep keep replace keep keep keep keep keep
 Access settings lazily, not at module import 
rest_framework/fields.py