谈谈python的文件处理——文件的输入与输出
谈谈python的文件处理——文件的输入与输出
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.从命令行中完成输入(与命令行的“博弈”——raw_input函数)
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#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) #一种输出变量内容的方式
#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.
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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.传递参数给代码(来自参数的“阅读”——将变量传递给脚本)
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#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
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3.文件读取(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。
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#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.
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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:
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• 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。
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清空文件,并重写文件
Example:
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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()
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2.其他文件操作——八仙过海,各显神通
文件拷贝
Example:
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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()
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文件和函数相结合
Example:
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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)
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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)
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