code: def incr(self, conn, key, increment=1):
          
          assert self._validate_key(key)
          resp = yield from self._incr_decr(
              conn, b'incr', key, increment)
          return resp
docs: Command is used to change data for some item in-place,
          incrementing it. The data for the item is treated as decimal
          representation of a 64-bit unsigned integer.
  
          :param key: ``bytes``, is the key of the item the client wishes
          to change
          :param increment: ``int``, is the amount by which the client
          wants to increase the item.
          :return: ``int``, new value of the item's data,
          after the increment or ``None`` to indicate the item with
          this value was not found