du.py

#!/usr/bin/env python

from os.path import getsize, isdir, exists, join
from os import walk

def main(argv=None):
    import sys
    from argparse import ArgumentParser

    argv = argv or sys.argv

    parser = ArgumentParser(description="Disk usage")
    parser.add_argument("root", help="root path")
    args = parser.parse_args(argv[1:])

    if not exists(args.root):
        raise SystemExit("error: can't find %s" % args.root)

    if isdir(args.root):
        total = 0
        for root, dirs, files in walk(args.root):
            for file in files:
                total += getsize(join(root, file))
    else:
        total = getsize(args.root)

    print(total/1024)

if __name__ == "__main__":
    main()