code: def set_datetime_format(self, format):
          
          if not format in ["UNIX", "RFC3339"]:
              return
  
          self.datetime_format = format
  
          self.set_header("Accept-Datetime-Format", self.datetime_format)
docs: Set the Accept-Datetime-Format header to an acceptable
          value
  
          Args:
              format: UNIX or RFC3339