使用“raise from”语法时对链接异常的完全回溯

Question

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

这方面的主要问题是，只有“链”中的“最高”错误的回溯（MySecondError），没有关于包装错误的信息（MyError）

如果我删除最后的try/except包装器以便不捕获链式错误，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

它具有完整错误链和连接行（Traceback (most recent call last):，The above exception was the direct cause of the following exception:）的回溯和每个错误的字符串表示

理想情况下，我希望捕获这些输出行以将它们定向到其他位置（例如记录器）

我的一个解决方案是迭代error.__context__并手动添加连词：

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__

这是可行的，但它是黑客的，我更愿意使用一些标准的库模块，它已经处理了这个问题

Answer 1

您想使用^{}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，此函数将不打印连接异常，而只打印最后一个异常