请问sys.argv的用法

请教sys.argv的用法
在《笨方法学python》第十五章的练习有：
from sys import argv

script, filename = argv

txt = open(filename)

print "Here's your file %r:" % filename
print txt.read()

print "Type the filename again:"
file_again = raw_input("> ")

txt_again = open(file_again)

print txt_again.read()

但是我在使用python 2.5 IDLE 执行到 script,filename =argv就出现问题，
Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
  script, filename = argv
ValueError: need more than 1 value to unpack

在google搜索了一下，没有相关的说明，麻烦帮忙指正下。谢谢

[解决办法]

Python code

python script.py arg