Modular exponentiation

powmod.py

from __future__ import print_function
import sys
import getopt
import math

g = None
e = None
m = None

argv = sys.argv[1:]
opts, args = getopt.getopt(argv, "g:e:m:")
for opt, arg in opts:
    if opt == '-g':
        g = int(arg)
    elif opt == '-e':
        e = int(arg)
    elif opt == '-m':
        m = int(arg)
    else:
        raise Exception("Unrecognised option: {0}".format(opt))

if args:
    raise Exception("Not matching options: {0}".format(args))

if e is None:
    e = m

if not all((g, e, m)):
    raise Exception("Must specify at least -g and -m, neither can be zero")

for i in range(e):
    print("{0}^{1:<{width}} mod {2} = {3}".format(g, i, m, pow(g, i, m),
                                                  width=int(math.ceil(math.log10(e)))))