Calculate password from cookie for Cisco router

cookie.py

#! /usr/bin/python3

# Copyright (C) 2018 Karim Kanso. All Rights Reserved.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

import sys

words = 8

def err() :
    print("Usage: ", sys.argv[0], " ", end="", file=sys.stderr)
    for i in range(words) :
        print("hh ll ", end="", file=sys.stderr)
    print("", file=sys.stderr)
    print("Calculates the cookie for cisco routers, copy the {} words from the cookie onto the command line.\n\thh = high byte in hex\n\tll = low byte in hex".format(words))
    sys.exit(1)

def main() :
    if len(sys.argv) != words * 2 + 1 :
        err()
    accumulator = 0
    try :
        for i in range(words) :
            h = int(sys.argv[1 + i * 2], base=16)
            l = int(sys.argv[(i+1) * 2], base=16)
            w = l + (h << 8)
            accumulator += w
    except ValueError as ve :
        print("Unable to process cookie value: {}".format(ve), file=sys.stderr)
        err()
    result = "{0:x}".format(accumulator)
    if len(result) < 4 :
        print("Error, failed to calculate accumulator of sufficient size: {}".format(result), file=sys.stderr)
        err()
    print("Done, result: ", result[-4:])

if __name__ == "__main__" :
    main()