程序代码：

class ShortInputException(Exception):
    '''a user-defined exception class.'''
    def __int__(self,length,atleast):
        Exception.__int__(self)
        self.length=length
        self.atleast=atleast
try:
    s=raw_input('enter something-->')
    if len(s)<3:
        raise ShortInputException(len(s),3)
except EOFError:
    print '\nwhy did you do an EOF on me?'
except ShortInputException,x:
    print 'ShortInputException:The input was of length %d,\
          was expectiing at least %d' %(x.length,x.atleast)
else:
    print 'no exception was raised.'