1.自定義異常類，自定義的異常類必須是Exception或者Error的子類！

 1 #!/usr/bin/env python
 2 # encoding: utf-8
 3 
 4 class IllegalException(Exception):
 5     ‘‘‘
 6     Custom exception types
 7     ‘‘‘
 8     def __init__(self, parameter, para_value):
 9         err = ‘The parameter "{0}" is not legal:{1}‘.format(parameter, para_value)
 
10         Exception.__init__(self, err)
11         self.parameter = parameter
12         self.para_value = para_value

2.try中使用raise語句來引發一個異常，其中check_positive_int(para_list)函數是用來檢查輸入的list是否為正整數。

 1 def check_positive_int(para_list):
 2         ‘‘‘
 3         @summary: check whether the parameter is positive integer
 
 4         @param: para_list: a list,para_list: a list,[{‘key‘:‘para1‘,‘value‘:para1},{‘key‘:‘para2‘,‘value‘:para2}]
 5         ‘‘‘
 6         for item in para_list:
 7             if not (item[‘value‘] > 0 and isinstance(item[‘value‘], int)):
 8                 return item[‘key‘], ‘{0} is not a positive integer
 
‘.format(str(item[‘value‘]))
 9         return True
10 
11 
12 try:
13     integer = check_positive_int([{‘key‘:‘para1‘, ‘value‘:1}, {‘key‘:‘para2‘, ‘value‘:-2}])
14     if integer != True:
15         raise(IllegalException(integer[0], integer[1]))
16 except IllegalException, x:
17     print ‘x--->‘, x
18     print ‘x.parameter--->‘, x.parameter
19     print ‘x.para_value--->‘, x.para_value
20 else:
21     print ‘NO ERROR‘

3.執行try，由於我們要校驗的list[{‘key‘:‘para1‘, ‘value‘:1}, {‘key‘:‘para2‘, ‘value‘:-2}]中有負數值，所以raise我們自定義的異常。

輸出結果為：

1 x---> The parameter "para2" is not legal:-2 is not a positive integer
2 x.parameter---> para2
3 x.para_value---> -2 is not a positive integer

python自定義異常，使用raise引發異常