如何用python的Try finally语句和with语句安全的读文件

Try...finally语句

输入：

#!/usr/bin/python

# Filename: finally.py

import time

try:

f = open('poem.txt')

while True:

# our usual file-reading idiom

line = f.readline()

if len(line) == 0:

break

print(line, end='')

time.sleep(2)

# To make sure it runs for a while

except KeyboardInterrupt:

print('!! You cancelled the reading from the file.')finally:

f.close()

print('(Cleaning up: Closed the file)')

输出：

$ python finally.py

Programming is fun

When the work is done

if you wanna make your work also fun:

!! You cancelled the reading from the file.

(Cleaning up: Closed the file)

解释：

当我们进行文件的操作时，为了保证有异常事件发生时，我们可以正常的关闭文件，所有我们使用了 try...finally函数。当有异常时，抛出异常，并且关闭文件操作。

本例中先打开文件操作，然后读文件，为了延长 try里运行时间，我们加入了sleep（2）停顿两秒时间，在此期间我们通过强制的 Ctrl C操作来人为的制造中断，造成异常，进入finally正常的执行了文件的关闭操作。

with语句

输入：

#!/usr/bin/python

# Filename: using_with.py

with open("poem.txt") as f:

for line in f:

print(line, end='')

输出：

$ python using_with.py

Programming is fun

When the work is done

解释:

与try...finally语句的功能一样，with函数也能够进行保护文件的正常操作。在遇到异常时，进行文件关闭。