code: def decr(self, key, value):
          
          server = self._get_server(key)
          return server.decr(key, value)
docs: Decrement a key, if it exists, returns it's actual value, if it don't, return 0.
          Minimum value of decrement return is 0.
  
          :param key: Key's name
          :type key: six.string_types
          :param value: Number to be decremented
          :type value: int
          :return: Actual value of the key on server
          :rtype: int