Python 2和3中捕获的异常实例的范围 [英] Scope of caught exception instance in Python 2 and 3

问题描述

由于Python变量可以在其循环之外访问，并且 try --块除外，因此我天真的认为这下面的代码段可以正常工作，因为可以访问 e ：

Since in Python variables are accessible outside of their loops and try-except blocks, I naively thought that this code snippet below would work fine because e would be accessible:

try:
    int('s')
except ValueError as e:
    pass
print(e)

在Python 2（经过2.7测试）中，它确实按预期工作，输出为：

In Python 2 (2.7 tested), it does work as I expected and the output is:

invalid literal for int() with base 10: 's'

但是，在Python 3让我惊讶的是输出是：

However, in Python 3 I was surprised that the output is:

NameError: name 'e' is not defined

为什么？

推荐答案

后来我找到了答案，因为 PEP 3110 解释说在Python 3中名称在 except 套件的末尾删除，以实现更有效的垃圾收集。如果您希望避免这种情况的发生，还建议使用语法：

I later found an answer as PEP 3110 explains that in Python 3 the caught name is removed at the end of the except suite to enable more efficient garbage collection. There is also recommended syntax if you wish to avoid this occurring:

需要在
附近保持异常实例的情况

Situations where it is necessary to keep an exception instance around past the end of the except suite can be easily translated like so

try:
    ...
except E as N:
    ...
...

try:
    ...
except E as N:
    n = N
    ...
…

这样，当N的末尾被删除时块，n将保留
并可以正常使用。

This way, when N is deleted at the end of the block, n will persist and can be used as normal.

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