python——异常类型

1 try：
2     print("try...")
3     s = 10/0 #异常，之后代码不执行
4     print("not run this code")
5 except ZeroDivisonError as e: #有错误执行一下语句
6     print("except",e)
7 finally:
8     print("finally...") # 有没有错误都要执行finally；此处可以不加
9 print("END")

1 try：
2     f = open("unexsit.file","r") 
3     f.read()
4 except Exception as e:
5     print("出错了，但是什么类型呢，打印一下吧"，e)
6 
7 #[Errno 2] No such file or directory: unexsit.file

 1 x=9
 2 
 3 def test():
 4     print(x)#
 5     x =1#python从上到下解释，会吧x当做局部变量，然而上边print要打印未声明的局部变量，报错
 6 
 7 test()
 8 #UnboundLocalError: local variable ‘x‘ referenced before assignment
 9 //修改
10 x=9
11 def test():
12     global x
13     print(x)
14     x =1
15 
16 test()

 1 It can be a surprise to get the UnboundLocalError in previously working code when it is modified by adding an assignment statement somewhere in the body of a function.
 2 
 3 This code:
 4 
 5 >>>
 6 >>> x = 10
 7 >>> def bar():
 8 ...     print x
 9 >>> bar()
10 10
11 works, but this code:
12 
13 >>>
14 >>> x = 10
15 >>> def foo():
16 ...     print x
17 ...     x += 1
18 results in an UnboundLocalError:
19 
20 >>>
21 >>> foo()
22 Traceback (most recent call last):
23   ...
24 UnboundLocalError: local variable ‘x‘ referenced before assignment
25 This is because when you make an assignment to a variable in a scope, that variable becomes local to that scope and shadows any similarly named variable in the outer scope. Since the last statement in foo assigns a new value to x, the compiler recognizes it as a local variable. Consequently when the earlier print x attempts to print the uninitialized local variable and an error results.
26 
27 In the example above you can access the outer scope variable by declaring it global:
28 
29 >>>
30 >>> x = 10
31 >>> def foobar():
32 ...     global x
33 ...     print x
34 ...     x += 1
35 >>> foobar()
36 10
37 This explicit declaration is required in order to remind you that (unlike the superficially analogous situation with class and instance variables) you are actually modifying the value of the variable in the outer scope:
38 
39 >>>
40 >>> print x
41 11

 1 class MyException(Exception):
 2     def __init__(self,name):
 3         self.msg = name
 4 
 5     def __str__(self):
 6        return self.msg # 可以不重写，继承基类
 7 
 8 #调用
 9 try:
10     if flag:
11         pass
12     else:
13         raise MyException("自定义错误")
14 except MyException as e:
15     print(e)