调试一个引发异常的程序

代码：

#!/usr/bin/env 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.'

单步执行程序，在执行到s=raw_input()的时候，跳转到App.py的Win32RawInput()函数，弹出输入窗口，输入少于3个字符以后，跳转到if len()语句，由于长度小于3，所以执行raise语句，跳转到ShortInputException类，初始化以后跳转到try下面的except EOFError语句，当前条件不符合，所以继续跳转到下一个except语句，并且执行except ShortInputException里的语句。

注：x是ShortInputException类的实例。