python - 使用 'raise from'语法时对链式异常的完整追溯

给定文件errors.py:

from traceback import format_tb, extract_tb

class MyError(Exception):
    def __init__(self, message):
        self.message = message

class MySecondError(Exception):
    def __init__(self, message):
        self.message = message

try:
    try:
        raise MyError("Something specific has happened")
    except Exception as error:
        raise MySecondError("Something general has happened") from error
except Exception as error:
    print("".join(format_tb(error.__traceback__)))

运行python errors.py时，输出为:

  File "errors.py", line 15, in <module>
    raise MySecondError("Something general has happened") from error

这样做的主要问题是，仅对“链”中的“最高”错误(MySecondError)进行追溯，而没有关于包装错误的信息(MyError)

如果删除最终的try/except包装程序，以便不捕获链接的错误，我会得到更好的输出:

Traceback (most recent call last):
  File "exceptions.py", line 14, in <module>
    raise MyError("Something specific has happened")
__main__.MyError: Something specific has happened

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

Traceback (most recent call last):
  File "exceptions.py", line 16, in <module>
    raise MySecondError("Something general has happened") from error
__main__.MySecondError: Something general has happened

具有完整错误链和联合行(Traceback (most recent call last):，The above exception was the direct cause of the following exception:)，每个错误的和字符串表示的追溯

理想情况下，我想捕获这些输出行以将它们定向到其他位置(例如记录器)

我拥有的一种解决方案是遍历error.__context__并手动添加连接短语:

except Exception as error:
    inner_error = error

    while inner_error:
        if inner_error is not error:
            print("\nThe above exception was the direct cause of the following exception:\n")

        print("Traceback (most recent call last):")
        print("".join(format_tb(inner_error.__traceback__) + [ str(error) ]))
        inner_error = inner_error.__context__

哪个可行，但是很麻烦，我希望使用一些已经可以解决此问题的标准库模块。

最佳答案

您想使用 format_exception 函数:

from traceback import format_tb, format_exception

class MyError(Exception):
    def __init__(self, message):
        self.message = message

class MySecondError(Exception):
    def __init__(self, message):
        self.message = message

try:
    try:
        raise MyError("Something specific has happened")
    except Exception as error:
        raise MySecondError("Something general has happened") from error
except Exception as error:
    print("".join(format_exception(error.__class__, error, error.__traceback__)))

给出:

$ python3 /tmp/a.py
Traceback (most recent call last):
  File "/tmp/a.py", line 13, in <module>
    raise MyError("Something specific has happened")
MyError: Something specific has happened

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

Traceback (most recent call last):
  File "/tmp/a.py", line 15, in <module>
    raise MySecondError("Something general has happened") from error
MySecondError: Something general has happened

如果指定chain=False，则此函数将不打印联合异常，而仅显示最后一个异常。

关于python - 使用 'raise from'语法时对链式异常的完整追溯，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/56604481/