python 精练（1）

#/usr/bin/python env
from os import listdir , sep 
from os.path import abspath, basename, isdir 
from sys import argv 

def tree(dir, padding, print_files=False):
    print padding[:-1] + '+-' + basename(abspath(dir)) + '/'
    padding = padding + ' '
    files = []
    if print_files:
        files = listdir(dir)
    else:
        files = [ x for x in listdir(dir) if isdir(dir + sep +x)]
    count = 0 
    for file in files:
        count +=1 
        print padding + '|'
        path = dir + sep + file 
        if isdir(path):
            if count == len(files):
                tree(path, padding + ' ', print_files)
            else:
                tree(path, padding + '|', print_files)
        else:
            print padding + '+-' + file 
def usage():
        return '''Usage: %s [-f] <path>
print tree structure of path specified.
options:
-f           print files as well as directories
path      path to process'''  % basename(argv[0])

def main():
    if len(argv) == 1:
        print usage()
    elif len(argv) == 2:
        path = argv[1]
        if isdir(path):
            tree(path, ' ')
        else:
            print 'ERROR: \'' + path + '\' is not a diretory'
    elif len(argv) == 3 and argv[1] == '-f':
        path = argv[2]
        if isdir(path):
            tree(path, ' ', True)
        else: 
            print 'ERROR: \'' + path + ' \' is not   a dirctory'
        else:
            print usage()

if __name= '__main__':
    main()

    #较长的代码必须要有main（）主方法。