docs: def to_python(self):
          '''A :class:`datetime.datetime` object is returned.'''
  
          if self.data is None:
              return None
  
          # don't parse data that is already native
          if isinstance(self.data, datetime.datetime):
              return self.data
          elif self.use_int:
              return datetime.datetime.utcfromtimestamp(self.data / 1000)
          elif self.format is None:
              # parse as iso8601
              return PySO8601.parse(self.data)
          else:
              return datetime.datetime.strptime(self.data, self.format)