def add(self, key, column_parent, column, consistency_level):
    """
    Increment or decrement a counter.

    Parameters:
     - key
     - column_parent
     - column
     - consistency_level
    """
    self._seqid += 1
    d = self._reqs[self._seqid] = defer.Deferred()
    self.send_add(key, column_parent, column, consistency_level)
    return d
Increment or decrement a counter.

    Parameters:
     - key
     - column_parent
     - column
     - consistency_level