python用户自定义异常的实例讲解

class ShortInputException(Exception):
 def __init__(self, length, atleast):
  self.length = length
  self.atleast = atleast
def main():
 try:
  s = input('请输入 --> ')
  if len(s) < 3:
# raise引发一个你定义的异常
raise ShortInputException(len(s), 3)
 except ShortInputException as result:#x这个变量被绑定到了错误的实例
  print('ShortInputException: 输入的长度是 %d,长度至少应是 %d'% (result.length, result.atleast))
 else:
  print('没有异常发生')
main()

#1.用户自定义异常类型，只要该类继承了Exception类即可，至于类的主题内容用户自定义，可参考官方异常类
class TooLongExceptin(Exception):
  "this is user's Exception for check the length of name "
  def __init__(self,leng):
 self.leng = leng
  def __str__(self):
 print("姓名长度是"+str(self.leng)+"，超过长度了")

 #1.捕捉用户手动抛出的异常，跟捕捉系统异常方式一样
def name_Test():
  try:
 name = input("enter your naem:")
 if len(name)>4:
raise TooLongExceptin(len(name))
 else :
print(name)
 
  except TooLongExceptin,e_result: #这里异常类型是用户自定义的
 print("捕捉到异常了")
 print("打印异常信息：",e_result)
 
#调用函数，执行
name_Test()
==========执行结果如下：==================================================
enter your naem:aaafsdf
捕捉到异常了
Traceback (most recent call last):
打印异常信息： 姓名长度是7，超过长度了
姓名长度是7，超过长度了
 File "D:/pythoyworkspace/file_demo/Class_Demo/extion_demo.py", line 16, in name_Test
  raise TooLongExceptin(len(name))
__main__.TooLongExceptin: <exception str() failed>
 
During handling of the above exception, another exception occurred:
 
Traceback (most recent call last):
 File "D:/pythoyworkspace/file_demo/Class_Demo/extion_demo.py", line 26, in <module>
  name_Test()
 File "D:/pythoyworkspace/file_demo/Class_Demo/extion_demo.py", line 22, in name_Test
  print("打印异常信息：",e_result)
TypeError: __str__ returned non-string (type NoneType)