lower/upper

lower.py

#!/usr/bin/env python3
import sys
import os


def main(args, f):

    if args:
        print(' '.join([f(x) for x in args]))
        return

    for line in sys.stdin:
        print(f(line))


if __name__ == '__main__':
    if os.path.basename(sys.argv[0]) == 'lower':
        main(sys.argv[1:], lambda x: x.lower())
    else:
        main(sys.argv[1:], lambda x: x.upper())