编写一个Python脚本，实现为重要的文件或文件夹在指定的目录下创建备份。

[设计思路]
[1] 将需要备份的文件和目录由一个列表指定，通过传入参数获得并保存到列表中。
[2] 备份应该保存在主备份目录中。
[3] 将文件备份成一个压缩文件。
[4] 每一次备份都根据当前的日期在主备份目录中创建一个子文件夹，而所备份的文件命名为当期的时间保存在这个子文件夹中。
[5] 压缩命令由本地用户决定。可以使用任何本地的存档压缩命令，只要它有命令行界面就可以了，那样就可以从脚本中传递参数给它。

[参考]
[1] A Byte of Python, 2005
[2] Python Manuals 2.6

    #! /usr/bin/python        # Filename: backup_ver1.py        # 2010-7-12 wcdj        import os        import time        import sys        # 1, The files and directories to be backed up are specified in a list        # source = ['/home/wcdj/my_prog', '/home/wcdj/local_installed']        # The following information is the debug used        print '--------------------------------'        source=[]        print 'The command line arguments are: '        for i in sys.argv:            print i            if i == sys.argv[0]:                continue            source.append(i)        print source        print '--------------------------------'        # check input, if error app exit        if len(source) == 0:            print '''''You should input the files or directories, like       python backup_ver1.py /home/wcdj/myfile /home/wcdj/mydir ...'''            exit()        else:            print 'Some files or directorier will be saved into .tar.gz format: '            print source        # If you are using Windows, use         # source=[r'c:/Documents', r'd:/work'] or         # source=['c://Documents', 'd://work'] or         # something like that        # 2, The backup must be stored in a main backup directory        # Remember to change this to what you will be using        target_dir = '/home/wcdj/backup/'        # 3, The files are backed up into a tar file        # 4, The name of subdirectory and tar file        today = target_dir + time.strftime('%Y%m%d')        now = time.strftime('%H%M%S')        # Take a comment from the user to create the name of the tar file        comment = raw_input('Enter a comment: ')        if len(comment) == 0:# check if a comment was entered            target = today + os.sep + now + '.tar.gz'        else:            target = today + os.sep + now + '_' + /            comment.replace(' ', '_') + '.tar.gz'        #Create the subdirectory if it isn't already there        if not os.path.exists(today):            os.mkdir(today)# make directory            print 'Successfully created directory', today        # 5, We use the tar command(in Unix/Linux) to put the files in a tgz archive        tar_command = "tar -zcf %s %s" % (target, ' '.join(source))        # Run the backup        if os.system(tar_command) == 0:            print 'Successful backup to', target        else:            print 'Backup failed'        # end