Python基础之语法错误和异常详解

时间:2022-11-03 18:01:53

一、前言

Python assert(断言)用于判断一个表达式,在表达式条件为 false 的时候触发异常。

Python基础之语法错误和异常详解

二、异常

即便 Python 程序的语法是正确的,在运行它的时候,也有可能发生错误。运行期检测到的错误被称为异常

三、异常处理

3.1 try/except

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try:
    # age_str = input("====>")
    # age = int(age_str)
 
    # l1 = []
    # l1[2]
 
    d1 = {}
    d1["name"]
 
except ValueError as e:
    print(e)
except IndexError as e:
    print(e)
except KeyError as e:
    print("KeyError:", e)
except Exception as e:
    print("其他未知异常")

3.2 try/except ... else

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# 异常的其他结构
s = "a"
s = 1
try:
    int(s)
except ValueError as e:
    print(e)
except KeyError as e:
    print(e)
except IndexError as e:
    print(e)
except Exception as e:
    print("捕获未知异常")
else:
    print("try 包含的代码块没有异常,执行else 里面的代码")
finally:
    print("执行finally 的代码,通常用于释放资源")

3.3 try-finally

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s = "a"
try:
    int(s)
except ValueError as e:
    print(e)
finally:
    print("执行finally 的代码,通常用于释放资源")

四、抛出异常

4.1 raise

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# 主动触发异常
try:
    raise TypeError("这个异常是主动触发的")
except TypeError as e:
    print(e)

五、用户自定义异常

自定义异常需要继承自 BaseException; (Exception 也 继承自 BaseException)

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# 自定义异常
class MyException(BaseException):
    def __init__(self, msg):
        self.msg = msg
 
    def __str__(self):
        return "<MyException:{}>".format(self.msg)
 
try:
    raise MyException("自定义异常")
except MyException as e:
    print(e)

六、断言 assert

程序某处判断结果,如果判断结果为 False; 抛出 AssertionError, 效果相当于 if 进行判断,再抛出异常

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assert 1 == 2
 
if 1 != 2:
    raise AssertionError

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原文链接:https://blog.csdn.net/qq_30346413/article/details/116881550