def is_seq_num(self, val):
        if val.isdigit():
            num = int(val)
            if num < 0: # 0 is a valid uid...
                raise SyntaxError("message sequence numbers " \
                                  "must be greater then 0: %d" % num)
            return num

        # We allow '*' as a message sequence number.
        if val == '*':
            return val

        # Otherwise return None.
        return None

    #######################################################################
    #
sequence_num ::= nz_number / "*"
dataset/ETHPy150Open scanner/asimap/asimap/parse.py/IMAPClientCommand.is_seq_num