Lists files and directories (like `ls` command does)

ls.py

import sys, os

try:
    root = sys.argv[1];
except IndexError:
    root = '.'

for dirname, dirnames, filenames in os.walk(root):
    for subdirname in dirnames:
        print os.path.join(dirname, subdirname)
    for filename in filenames:
        print os.path.join(dirname, filename)