code: def multi(self):
          
          if self.explicit_transaction:
              raise RedisError('Cannot issue nested calls to MULTI')
          if self.command_stack:
              raise RedisError('Commands without an initial WATCH have already '
                               'been issued')
          self.explicit_transaction = True
docs: Start a transactional block of the pipeline after WATCH commands
          are issued. End the transactional block with `execute`.