gcd.py

#!/usr/bin/env python
#
# Get two numbers from user, print their gcd (Greatest Common Divisor).
#
# Author:  Yotam Medini  [email protected] -- Created: 2005/June/19
#

import sys
import string

# Check for 2 parameters
if len(sys.argv) != 3:
    sys.stderr.write("I should be called with 2 parameters!\n")
    sys.stderr.write("Usage:  %s <number> <number>\n" % sys.argv[0])
    sys.exit(1)

# Convert the two command line parameters strings to integer numbers.
a = int(sys.argv[1])
b = int(sys.argv[2])

sys.stdout.write("gcd(%d,%d) = " % (a, b)); # The result will come soon...

# If any is negative, convert it to positive.
# It does not change the gcd(a,b) result !!
if a < 0:
    a = -a
if b < 0:
    b = -b

# Let's always have a >= b
if a < b:
    # swap  a <-> b
    temp = a
    a = b
    b = temp

if a == 0:
    # Since a >= b >= 0, we must have b == 0.
    # Any non-zero integer divides 0, and so:
    sys.stdout.write("Infinity\n")

else:

    # Now the beautiful Euclid algorithm. Short and smart.
    while b != 0:
        residue = a % b
        a = b
        b = residue
    sys.stdout.write("%d\n" % a)

sys.exit(0)