引发异常

#!/usr/bin/python
#Filename:raising.py


class ShortInputException(Exception):
    '''A user-defined exception class.'''
    def __init__(self,length,atleast):
        Exception.__init__(self)
        self.length=length
        self.atleast=atleast


try:
    s=raw_input('Enter something->')
    if len(s)<3:
        raise ShortInputException(len(s),3)
    # 0 ther work can continue as usual here except EOFError:
except EOFError:
    print '\n Why did you do an E0F 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.'

自定义异常ShortInputEcception，注意init前面是两个小横杆，异常类型EOFError全是英文字母。