第11章文件

11.1 打开文件
open

11.2 文件的基本方法
三个标准流：
标准数据输入源：sys.stdin
输出：sys.stdout
错误输出：sys.stderr

11.2.1 读取和写入

>>> f = open('f://somefile.txt','w')
>>> f.write('Hello,')
6
>>> f.write('World!')
6
>>> f.close()
>>> f = open('f://somefile.txt','r')
>>> f.read(4)
'Hell'
>>> f.read()
'o,World!'
>>> f.close()
>>>

11.2.2 使用管道重定向输出

#wordcount.py
#计算sys.stdin中包含多少个单词的简单脚本
import sys
text = sys.stdin.read()
words = text.split()
wordcount = len(words)
print('wordcount:',word)

cat somefile.txt | python wordcount.py

11.2.3 读取和写入行
readlines 和 writelines

11.2.4 关闭文件
close将文件关闭。

#在这里打开文件
try:
    # 将数据写入到文件中
finally:
    file.close()

#with语句
with open("somefile.txt") as somefile:
    do_something(somefile)

11.2.5 使用文本的基本方法

>>> f = open(r'f:\somefile.txt')
>>> f.read(7)
'Welcome'
>>> f.read(4)
' to '
>>> f.close()
>>> f = open(r'f;\somefile.txt')
Traceback (most recent call last):
  File "<pyshell#16>", line 1, in <module>
    f = open(r'f;\somefile.txt')
FileNotFoundError: [Errno 2] No such file or directory: 'f;\\somefile.txt'
>>> f = open(r'f:\somefile.txt')
>>> f.read()
'Welcome to this file\nThere is nothing here except\nThis stupid haiku'
>>> f.close()
>>> f = open(r'f:\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.readlines()
[]
>>> f.close()
>>> f = open(r'f:\somefile.txt')
>>> f.readlines()
['Welcome to this file\n', 'There is nothing here except\n', 'This stupid haiku']
>>> f.close()
>>> f = open(r'f:\somefile.txt')
>>> f.write('this\nis\nhaiku')
Traceback (most recent call last):
  File "<pyshell#30>", line 1, in <module>
    f.write('this\nis\nhaiku')
io.UnsupportedOperation: not writable
>>> f.close()
>>> f = open(r'f:\somefile.txt','w')
>>> f.write('this\nis no\nhaiku')
16
>>> f.close()
>>>

11.3 迭代文件内容

11.3.1 每次一个字符（或字节）

#使用read遍历字符
with open(r'f:somefile.txt') as f:
    char = f.read(1)
    while char:
        print("processing: ",char)
        char = f.read(1)

#以不同的方式编写循环
with open(r'f:somefile.txt') as f:
    while True:
        char = f.read(1)
        if not char: break
        print("processing:",char)

11.3.2 每次一行

#每次一行
with open(r'f:\somefile.txt') as f:
    while True:
        line = f.readline()
        if not line: break
        print("process:" + line)

11.3.3 读取所有内容

#使用read迭代字符
with open(r'f:\somefile.txt') as f:
    for char in f.read():
        print("process: " + char)


#使用readlines迭代行
with open(r'f:\somefile.txt') as f:
    for line in f.readlines():
        print("process: " + line)

11.3.4 使用fileinput实现延迟行迭代
说它延迟是因为它只读取实际需要的文本部分。

#使用fileinput迭代行
import fileinput
for line in fileinput.input(r'f:\somefile.txt'):
    print("process: " + line)

11.3.5 文件迭代器（最酷最常见的方法）

#迭代文件
with open(r'f:somefile.txt') as f:
    for line in f:
        print("process: " + line)

11.4 小结

第11章 文件

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