python - 在 python 3 中禁用异常链接

Question

python3 引入了一个新特性——异常链。由于某些原因，我需要针对代码中的某些异常禁用它。

示例代码如下:

try:
    print(10/0)
except ZeroDivisionError as e:
    sys.exc_info()
    raise AssertionError(str(e))

我看到的:

Traceback (most recent call last):
  File "draft.py", line 19, in main
    print(10/0)
ZeroDivisionError: division by zero

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "draft.py", line 26, in <module>
    main()
  File "draft.py", line 22, in main
    raise AssertionError(str(e))
AssertionError: division by zero

我想看到的:

Traceback (most recent call last):
  File "draft.py", line 26, in <module>
    main()
  File "draft.py", line 22, in main
    raise AssertionError(str(e))
AssertionError: division by zero

我尝试使用 sys.exc_clear()，但此方法也已从 python 3 中删除。 我可以使用有效的解决方法

exc = None
try:
    print(10/0)
except ZeroDivisionError as e:
    exc = e
if exc:
    raise AssertionError(str(exc))

但我相信有更好的解决方案。

Answer 1

简单回答

try:
    print(10/0)
except ZeroDivisionError as e:
    raise AssertionError(str(e)) from None

但是，您可能真的想要:

try:
    print(10/0)
except ZeroDivisionError as e:
    raise AssertionError(str(e)) from e

说明

__cause__

当没有明确的原因异常集时，通过 __context__ 发生隐式异常链接。

显式异常链接通过 __cause__ 工作，因此如果您将 __cause__ 设置为异常本身，它应该停止链接。如果设置了 __cause__，Python 将抑制隐式消息。

try:
    print(10/0)
except ZeroDivisionError as e:
    exc = AssertionError(str(e))
    exc.__cause__ = exc
    raise exc

来自

我们可以使用“raise from”来做同样的事情:

try:
    print(10/0)
except ZeroDivisionError as e:
    exc = AssertionError(str(e))
    raise exc from exc

无 __cause__

将 __cause__ 设置为 None 实际上做了同样的事情:

try:
    print(10/0)
except ZeroDivisionError as e:
    exc = AssertionError(str(e))
    exc.__cause__ = None
    raise exc

从无加注

因此，这将我们带到最优雅的方式来做到这一点，即从None筹集资金:

try:
    print(10/0)
except ZeroDivisionError as e:
    raise AssertionError(str(e)) from None

但我认为您通常希望从原因异常中显式引发异常，以便保留回溯:

try:
    print(10/0)
except ZeroDivisionError as e:
    raise AssertionError(str(e)) from e

这将给我们一个稍微不同的消息，指出第一个异常是第二个异常的直接原因:

Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
ZeroDivisionError: division by zero

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
AssertionError: division by zero