@acquire<EOL><INDENT>def incr(self, conn, key, increment=<NUM_LIT:1>):<DEDENT>
assert self._validate_key(key)<EOL>resp = yield from self._incr_decr(<EOL>conn, b'<STR_LIT>', key, increment)<EOL>return resp<EOL>
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