code: def duration(self):
          
          if self.ended_timestamp is None:
              return datetime.datetime.utcnow() - self.message.created_at
          else:
              return self.ended_timestamp - self.message.created_at
docs: Queries the duration of the call.
  
          If the call has not ended then the current duration will
          be returned.
  
          Returns
          ---------
          datetime.timedelta
              The timedelta object representing the duration.