还原 python 中的更改 try exception block before raising

Question

我需要为单个验证更新对象的一个属性。在任何情况下，我都需要在验证引发错误之前恢复它。我目前很困惑，如果这实际上是在异常引发之前恢复某些东西的最漂亮的方法，因为那时我必须复制恢复代码。 finally 在这里不起作用，因为它是在 raise 语句之后执行的。

amount = instance.amount
instance.amount = 0
try:
    validate_instance(instance)
except Exception:
    instance.amount = amount
    raise
else:
    instance.amount = amount

Answer 1

最后block应该就可以了，如下图：

amount = 15

def throw_me_an_error():
    try:
        amount = 20
        print("I've set the amount to 20.")
        test = 'hey' + 1
    except Exception as e:
        print('Exception thrown')
        raise e
    else:
        print('Else part')
    finally:
        amount = 15
        print('I reverted the amount to 15.')
        print('Finally!')
        
try:
    throw_me_an_error()
except Exception:
    print('An exception was thrown')
    
print(f'The amount is now {amount}')

结果

I've set the amount to 20.
Exception thrown
I reverted the amount to 15.
Finally!
An exception was thrown
The amount is now 15

Answer 2

正如其他答案中指出的那样，最终确实可以正常工作：

>>> try:
...     try:
...         print(1)
...         x += 1
...     except Exception:
...         raise
...     finally:
...         print(2)
... except Exception:
...     print(3)
... 
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还原 python 中的更改 try exception block before raising

Revert changes in python try exception block before raising

python

pep8

code-duplication

python-3.x