python异常处理--try except else raise finally

超、凢脫俗 2023-10-08 08:47 53阅读 0赞

写程序时遇到异常情况，程序可能无法正常运行。此时就需要引入异常处理

1.try ...except

try 后面写正常运行的程序代码，except即为异常情况

![复制代码][aHR0cHM6Ly9jb21tb24uY25ibG9ncy5jb20vaW1hZ2VzL2NvcHljb2RlLmdpZg]

1 a=3
     2 b=2
     3 for i in range(5):
     4     try:
     5         a = a - 1
     6         c=b/a
     7         print(c)
     8 
     9     except Exception as e:
    10         print(e)#输出异常行为名称

![复制代码][aHR0cHM6Ly9jb21tb24uY25ibG9ncy5jb20vaW1hZ2VzL2NvcHljb2RlLmdpZg]

结果显示如下，异常行为的名称为（division by zero）

![format_png][]

2.try ....except...else 语句，当没有异常发生时，else中的语句将会被执行

![复制代码][aHR0cHM6Ly9jb21tb24uY25ibG9ncy5jb20vaW1hZ2VzL2NvcHljb2RlLmdpZg]

a=3
    b=2
    for i in range(3):
        try:
            a = a - 1
            c=b/a
            print(c)
    
        except Exception as e:
            print(e)
        else:
            print("正常运行")

![复制代码][aHR0cHM6Ly9jb21tb24uY25ibG9ncy5jb20vaW1hZ2VzL2NvcHljb2RlLmdpZg]

发生异常时，else的语句没有被运行

![format_png 1][]

**当执行try ...finally 语句时，**无论异常是否发生，在程序结束前，finally中的语句都会被执行。

![复制代码][aHR0cHM6Ly9jb21tb24uY25ibG9ncy5jb20vaW1hZ2VzL2NvcHljb2RlLmdpZg]

#Author:wang yue
    a=3
    b=2
    for i in range(3):
        try:
            a = a - 1
            c=b/a
            print(c)
    
        except Exception as e:
            print(e)
        else:
            print("正常运行")
        finally:
            print("finally")

![复制代码][aHR0cHM6Ly9jb21tb24uY25ibG9ncy5jb20vaW1hZ2VzL2NvcHljb2RlLmdpZg]

![format_png 2][]

4.raise引发一个异常，比如，当一个条件不满足用户意愿时引发一个异常

a=3
    if a<4:
        raise Exception

else: print(a)

![format_png 3][]

来源：[https://www.cnblogs.com/bokeyuan11/p/9146607.html][https_www.cnblogs.com_bokeyuan11_p_9146607.html]

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[https_www.cnblogs.com_bokeyuan11_p_9146607.html]: https://www.cnblogs.com/bokeyuan11/p/9146607.html