replace.py

import sys


def usage():
    sys.stdout.write('usage: replace.py pairing [pairing ...]')
    sys.stdout.write('    a pairing is a char and what to replace it with')
    sys.stdout.write('    e.g. replace.py a A would replace all \'a\' with \'A\'')
    sys.exit(1)


def group2(l):
    return zip(*[iter(l)]*2)


if len(sys.argv) < 2:
    usage()

args = sys.argv[1:]

if len(args) % 2 != 0:
    usage()

reps = {}
for argA, argB in group2(args):
    reps[argA] = argB

for line in sys.stdin.readlines():
    chunkbylen = {}
    for pair in reps:
        line = line.replace(pair, reps[pair])
    sys.stdout.write(line)
sys.exit(0)