code: def field_timedelta_to_json(self, td):
          
          if isinstance(td, six.string_types):
              td = parse_duration(td)
          if not td:
              return None
          if td.microseconds > 0:
              return str(td.total_seconds())
          else:
              return int(td.total_seconds())
docs: Convert timedelta to value containing total number of seconds.
  
          If there are fractions of a second the return value will be a
          string, otherwise it will be an int.