change values of two variables without third variable

ab.py

#!/usr/bin/env python

import sys


def main(a, b):
    print 'a = %d, b = %d' % (a, b)
    b ^= a
    a ^= b
    b ^= a
    print 'a = %d, b = %d' % (a, b)

if __name__ == '__main__':
    main(int(sys.argv[1]), int(sys.argv[2]))