Python基础（九）异常

 1 #基本语法为
 2 try:
 3     被检测的代码块
 4 except 异常类型：
 5     try中一旦检测到异常，就执行这个位置的逻辑
 6 
 7 #举例
 8 try:
 9     f=open(‘a.txt‘)
10     g=(line.strip() for line in f)
11     print(next(g))
12     print(next(g))
13     print(next(g))
14     print(next(g))
15     print(next(g))
16 except StopIteration:
17     f.close()

 1 #1 异常类只能用来处理指定的异常情况，如果非指定异常则无法处理。
 2 s1 = ‘hello‘
 3 try:
 4     int(s1)
 5 except IndexError as e: # 未捕获到异常，程序直接报错
 6     print e
 7 
 8 #2 多分支
 9 s1 = ‘hello‘
10 try:
11     int(s1)
12 except IndexError as e:
13     print(e)
14 except KeyError as e:
15     print(e)
16 except ValueError as e:
17     print(e)
18 
19 #3 万能异常Exception
20 s1 = ‘hello‘
21 try:
22     int(s1)
23 except Exception as e:
24     print(e)
25 
26 #4 多分支异常与万能异常
27 #4.1 如果你想要的效果是，无论出现什么异常，我们统一丢弃，或者使用同一段代码逻辑去处理他们，那么骚年，大胆的去做吧，只有一个Exception就足够了。
28 #4.2 如果你想要的效果是，对于不同的异常我们需要定制不同的处理逻辑，那就需要用到多分支了。
29 
30 #5 也可以在多分支后来一个Exception
31 s1 = ‘hello‘
32 try:
33     int(s1)
34 except IndexError as e:
35     print(e)
36 except KeyError as e:
37     print(e)
38 except ValueError as e:
39     print(e)
40 except Exception as e:
41     print(e)
42 
43 #6 异常的其他机构
44 s1 = ‘hello‘
45 try:
46     int(s1)
47 except IndexError as e:
48     print(e)
49 except KeyError as e:
50     print(e)
51 except ValueError as e:
52     print(e)
53 #except Exception as e:
54 #    print(e)
55 else:
56     print(‘try内代码块没有异常则执行我‘)
57 finally:
58     print(‘无论异常与否,都会执行该模块,通常是进行清理工作‘)
59 
60 #7 主动触发异常
61 try:
62     raise TypeError(‘类型错误‘)
63 except Exception as e:
64     print(e)
65 
66 #8 自定义异常
67 class EgonException(BaseException):
68     def __init__(self,msg):
69         self.msg=msg
70     def __str__(self):
71         return self.msg
72 
73 try:
74     raise EgonException(‘类型错误‘)
75 except EgonException as e:
76     print(e)
77 
78 #9 断言:assert 条件
79 assert 1 == 1  
80 assert 1 == 2