code: def xadd(self, stream, fields, message_id=b'*', max_len=None,
               exact_len=False):
          
          args = []
          if max_len is not None:
              if exact_len:
                  args.extend((b'MAXLEN', max_len))
              else:
                  args.extend((b'MAXLEN', b'~', max_len))
  
          args.append(message_id)
  
          for k, v in fields.items():
              args.extend([k, v])
          return self.execute(b'XADD', stream, *args)
docs: Add a message to a stream.