简单介绍一下python里IO的几种常用方式。当然除了以下介绍的几种方式之外，还可以参考python的手册，例如我想查找raw——input函数的用法，我就可以直接使用命令：python -m pydoc raw_input（windows底下）来查看使用方法，使用完毕时候，输入“q”作为退出。下面进入正题：
一、python中的输入
1.与命令行的“博弈”——raw_input函数
#Input： age = raw_input("How old are you? ") height = raw_input("How tall are you? ") weight = raw_input("How much do you weigh? ") print "So, you‘re %r old, %r tall and %r heavy." % (age, height, weight） #Output： How old are you? 35 How tall are you? 6‘2" How much do you weight? 180lbs So, you‘re ‘35‘ old, ‘6\‘2"‘ tall and ‘180lbs‘ heavy.
注意：这里 %r 是 debug 专用，它显示的是原始表示出来的字符；也会常常见到使用%s的情况， %s 是为了显示给用户看的字符串。
2.来自参数的“阅读”——将变量传递给脚本
#Input： from sys import argv script, first, second, third = argv print "The script is called:", script print "Your first variable is:", first print "Your second variable is:", second print "Your third variable is:", third #Output： python ex13.py cheese apples bread The script is called: ex13.py Your first variable is: cheese Your second variable is: apples Your third variable is: bread
3.倾听文件的“内容”——读取文件有妙招
假设我们现在有两个文件，一个是脚本文件 ex.py ，另外一个是 ex_sample.txt，第二
个文件是供你的脚本读取的文本文件。假设第二个文件的内容：
This is stuff I typed into a file.
It is really cool stuff.
Lots and lots of fun to have in here.
我们要做的是把该文件用我们的脚本“打开(open)”，然后打印出来。然而把文件名
ex_sample.txt 写死(hardcode)在代码中不是一个好主意，这些信息应该是用户输入的才对。如果我们碰到其他文件要处理，写死的文件名就会给你带来麻烦了。我们的解决方案是使用 argv 和raw_input 来从用户获取信息，从而知道哪些文件该被处理。
#Input： from sys import argv script, filename = argv txt = open(filename) print "Here‘s your file %r:" % filename print txt.read() #Output： python ex.py ex_sample.txt Here‘s your file ‘ex_sample.txt‘: This is stuff I typed into a file. It is really cool stuff. Lots and lots of fun to have in here.
延伸：txt = open(filename) 返回的是文件的内容吗？ 不是，它返回的是一个叫做“file object”的东西，你可以把它想象成一个磁带机或者 DVD 机。你可以随意访问内容的任意位置，并且去读取这些内容，不过这个 object 本身并不是它的内容。
二、读写文件
1.常用读写文件函数——韩信点兵：
• close – 关闭文件。跟你编辑器的 文件->保存.. 一个意思。
• read – 读取文件内容。你可以把结果赋给一个变量。
• readline – 读取文本文件中的一行。
• truncate – 清空文件，请小心使用该命令。
• write(stuff) – 将 stuff 写入文件。
清空文件，并重写文件
Example：
print "Opening the file..." target = open(filename, ‘w‘) print "Truncating the file. Goodbye!" target.truncate() print "Now I‘m going to ask you for three lines." line1 = raw_input("line 1: ") line2 = raw_input("line 2: ") line3 = raw_input("line 3: ") print "I‘m going to write these to the file." target.write(line1) target.write("\n") target.write(line2) target.write("\n") target.write(line3) target.write("\n") print "And finally, we close it." target.close()
2.其他文件操作——八仙过海，各显神通
文件拷贝
Example：
from sys import argv from os.path import exists script, from_file, to_file = argv print "Copying from %s to %s" % (from_file, to_file) # we could do these two on one line too, how? in_file = open(from_file) indata = in_file.read() print "The input file is %d bytes long" % len(indata) print "Does the output file exist? %r" % exists(to_file) print "Ready, hit RETURN to continue, CTRL-C to abort." raw_input() out_file = open(to_file, ‘w‘) out_file.write(indata) print "Alright, all done." out_file.close() in_file.close()
文件和函数相结合
Example：
from sys import argv script, input_file = argv def print_all(f): print f.read() def rewind(f): f.seek(0) def print_a_line(line_count, f): print line_count, f.readline() current_file = open(input_file) print "First let‘s print the whole file:\n" print_all(current_file) print "Now let‘s rewind, kind of like a tape." rewind(current_file) print "Let‘s print three lines:" current_line = 1 print_a_line(current_line, current_file) current_line = current_line + 1 print_a_line(current_line, current_file) current_line = current_line + 1 print_a_line(current_line, current_file)
其中seek（0），表示找到文件开始的位置。
附加：多行输出的方法
print """
Alright, so you said %r about liking me.
You live in %r. Not sure where that is.
And you have a %r computer. Nice.
""" % (likes, lives, computer)
原文：http://www.cnblogs.com/inspirationhyl/p/4023994.html