docs: def append(self, name, value):
          """
          Appends the string ``value`` to the value at ``key``. If ``key``
          doesn't already exist, create it with a value of ``value``.
          Returns the new length of the value at ``key``.
  
          :param name: str     the name of the redis key
          :param value: str
          :return: Future()
          """
          with self.pipe as pipe:
              return pipe.append(self.redis_key(name),
                                 self.valueparse.encode(value))