说明

1、程序可以通过创建一个新的异常类来命名它们自己的异常。异常应该是典型的继承自Exception类，直接或间接的方式。

2、异常python有一个大基类，继承了Exception。因此，我们的定制类也必须继承Exception。

实例

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()

知识点扩展：

自定义异常类型

#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")

捕捉用户手动抛出的异常

 #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)