Python异常处理，,我们可以使用try.

Python异常处理，,我们可以使用try.

我们可以使用try..except语句来处理异常。我们把通常的语句放在try-块中，而把我们的错误处理语句放在except-块中。

1.处理异常

#!/usr/bin/python# Filename: try_except.pyimport systry:        s = raw_input(‘Enter something --> ‘)except EOFError:        print ‘\nWhy did you do an EOF on me?‘        sys.exit() # exit the programexcept:        print ‘\nSome error/exception occurred.‘        # here, we are not exiting the programprint ‘Done‘

运行结果

# ./try_except.py    enterEnter something -->Done# ./try_except.py   ctrl+dEnter something -->Why did you do an EOF on me?

2.如何引发异常

#!/usr/bin/python# Filename: raising.pyclass ShortInputException(Exception):        ‘‘‘A user-defined exception class.‘‘‘        def __init__(self, length, atleast):                Exception.__init__(self)                self.length = length                self.atleast = atleasttry:        s = raw_input(‘Enter something --> ‘)        if len(s) < 3:                raise ShortInputException(len(s), 3)# Other work can continue as usual hereexcept EOFError:        print ‘\nWhy did you do an EOF on me?‘except ShortInputException, x:        print ‘ShortInputException: The input was of length %d, was expecting at least %d‘ % (x.length, x.atleast)else:        print ‘No exception was raised.‘

运行结果

[root@host python]# ./raising.pyEnter something --> ffShortInputException: The input was of length 2, was expecting at least 3[root@host python]# ./raising.pyEnter something --> 222No exception was raised.

这里，我们创建了我们自己的异常类型，其实我们可以使用任何预定义的异常/错误。这个新的异常类型是ShortInputException类。它有两个域——length是给定输入的长度，atleast则是程序期望的最小长度。

3.使用finally

#!/usr/bin/python# Filename: finally.pyimport timetry:        f = file(‘poem.txt‘)        while True: # our usual file-reading idiom                line = f.readline()                if len(line) == 0:                        break                time.sleep(2)                print line,finally:        f.close()        print ‘Cleaning up...closed the file‘

运行结果

# ./finally.pyProgramming is funWhen the work is doneif you wanna make your work also fun:use Python!Cleaning up...closed the file# ./finally.pyProgramming is funWhen the work is done^CCleaning up...closed the file      --ctrl+c to breakTraceback (most recent call last):  File "./finally.py", line 10, in <module>    time.sleep(2)KeyboardInterrupt

在程序运行的时候，按Ctrl-c中断/取消程序。我们可以观察到KeyboardInterrupt异常被触发，程序退出。但是在程序退出之前，finally从句仍然被执行，把文件关闭

Python异常处理