新手 看书疑问 问个问题...

#!/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)
    # Other work can continue as usual here
except 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.'



里面的except ShortInputException, x:  中 x 表示什么?  怎么 无缘无故就跑出来了...... 还有  类可以不用实例化 直接来用么??

x表示捕捉到的ShortInputException的实例
类是可以直接用的，具体的一句两句说不清楚，可以查看一下有关资料