第十一章 文件和素材
11.1 打开文件
open函数用来打开文件，语法如下：
open(name[,mode[,buffering]])
f = open(r'/home/python/somefile.txt')
11.1.1 文件模式
r 读模式
w 写模式
a 追加模式
b 二进制模式（可添加到其他的模式中）
+ 读写模式（可添加到其他的模式中）
在模式参数中使用U参数能够在打开文件时使用通用的换行符支持模式
11.1.2 缓冲
单位是字节，使用flush或者close时更新到磁盘
11.2 基本文件方法
sys.stdin
sys.stdout
sys.stderr 在文件对象中也可以使用
11.2.1 读和写
>>> f=open('somefile.txt','w')
>>> f.write('Hello,')
>>> f.write('World!')
>>> f.close()
>>> f=open('somefile.txt','r')
>>> f.read(4)
'Hell'
>>> f.read()
'o,World!'
11.2.2 管式输出
# cat somescript.py #!/usr/bin/env python #coding=utf-8 # somescript.py import sys text = sys.stdin.read() words = text.split() wordcount = len(words) print 'Wordcount:', wordcount
# cat somefile.txt Your mother was a hamster and your father smelled of elderberries.
# cat somefile.txt |python somescript.py Wordcount: 11
seek(offset[,whence])
tell方法返回当前文件的位置
11.2.3 读写行
file.readline 读取单独的一行
file.readline(5)
file.readlines
file.writelines 读取文件中所有的行并作为列表返回
file.write
没有writeline方法
11.2.4 关闭文件
try: #write data to your file fianlly: file.close() file.fush()
with open("somefile.txt") as somefile:
do_someting(somefile)
11.2.5 使用基本文件方法
读
cat somefile.txt Welcome to this file There is nothing here except This stupid haiku
>>> f=open('/home/mysql/somefile.txt')
>>> f.read(7)
'Welcome'
>>> f.read(4)
' to '
>>> f.close()
>>> f=open('/home/mysql/somefile.txt')
>>>
>>> print f.read()
Welcome to this file
There is nothing here except
This stupid haiku
>>> f.close()
>>> f=open('/home/mysql/somefile.txt')
>>> for i in range(3):
... print str(i)+":"+f.readline()
...
0:Welcome to this file
1:There is nothing here except
2:This stupid haiku
>> f.close()
>>> import pprint
>>> pprint.pprint(open('/home/mysql/somefile.txt').readlines())
['Welcome to this file\n',
'There is nothing here except\n',
'This stupid haiku\n']
写
$ cat somefile.txt this is no haiku >>> f=open(r'/home/mysql/somefile.txt') >>> line=f.readlines() >>> f.close() >>> line[1]="isn't a \n" >>> f=open(r'/home/mysql/somefile.txt','w') >>> f.writelines(line) >>> f.close() $ cat somefile.txt this isn't a haiku
11.3 对文件内容进行迭代
def process(string): print 'Processing:',string
11.3.1 按字节处理
用read方法对每个字符进行循环
f = open(filename) char = f.read(1) while char: process(char) char = f.read(1) f.close()
f = open(filename) while True: char = f.read(1) if not char: break process(char) f.close()
11.3.2 按行操作
f = open(filename) while True: line = f.readline() if not line: break process(line) f.close()
11.3.3 读取所有内容
如果文件不是很大，可以一次性读取
f = open(filename) for char in f.read(): process(char) f.close()
f = open(filename) for line in f.readlines(): process(line) f.close()
11.3.4 使用fileinput实现懒惰行迭代
fileinput 模块包含了打开文件的函数
import fileinput for line in fileinput.input(filename): process(line)
11.3.5 文件迭代器
f = open(filename) for line in f: process(line) f.close()
for line in open(filename): process(line)
import sys for line in sys.stdin: process(line)
可以对文件迭代器执行和普通迭代器相同的操作，list(open(filename))
>>> f=open(r'/home/mysql/somefile.txt','w')
>>> f.write('Fist line\n')
>>> f.write('Second line\n')
>>> f.write('Third line\n')
>>> f.close()
>>> lines=list(open('somefile.txt'))
>>> lines
['Fist line\n', 'Second line\n', 'Third line\n']
>>> first,second,third=open('somefile.txt')
>>> first
'Fist line\n'
>>> second
'Second line\n'
>>> third
'Third line\n'