python 异常处理

python中特殊的异常处理

通常Exception能捕捉所有异常,但这些异常必须为python内部自定义的异常(并且不包括BaseException);若程序中抛出自定义异常,或者BaseException则该异常不能被Exception捕捉;但可以被BaseException或者不带参数的except捕捉

class CustomException(BaseException):
    pass
try:
    raise CustomException('an error accured')
except Exception as e:
    print(f"catch exception {e}")

# 运行结果
Traceback (most recent call last):
  File "C:/Users/wyx/Desktop/test.py", line 108, in <module>
    raise CustomException('an error accured')
CustomException: an error accured

class CustomException(BaseException):
    pass

try:
    raise CustomException('an error accured')
except BaseException as e:
    print(f"catch exception '{e}'")

# 运行结果
catch exception 'an error accured'

with在异常发生时自动执行对象的__exit__方法

使用with进行上下文管理时,只要__enter__方法已经执行完成,无论执行过程中是否抛出异常,__exit__方法均会执行

class A:
    def __enter__(self):
        # raise BaseException('error in content')
        print('Enter class A')

    def __exit__(self,Type, value, traceback):
        print('exit class A')

with A():
    raise BaseException('error in content')

# 结果
Enter class A
exit class A
Traceback (most recent call last):
  File "C:/Users/wyx/Desktop/test.py", line 98, in <module>
    raise BaseException('error in content')
BaseException: error in content