python - 在 Python 中使用自定义异常动态扩展异常？

Question

假设我有一个特殊的异常(exception)，它做了一些整洁而美妙的事情 - 解决世界饥饿、对人类的善意、伐木等:

class SpecialException(Exception):
    # Does something really neat here.
    pass

现在假设可能会引发异常，但我们不知道会遇到什么类型的异常:

def crashAndBurn():
    try:
        import random
        choice = random.choice([1,2])
        if choice == 1:
            int('asdf') # Can't cast string to int: ValueError.
        else:
            x # Variable `x` doesn't exist: NameError.
    except Exception as e:
        # Code to wrap `e` into `SpecialException` class
        raise e

当引发未知类型的异常时，我们想要捕获它，将它包装在我们的 SpecialException 中。类，并提升它以便它可以被抛出的原始类型的异常捕获，或者通过捕获 SpecialException :

try:
    crashAndBurn()
except ValueError as e:
    print('This time it was a ValueError, and we want to handle this differently for some reason')
except SpecialException as e:
    print('Handle this more generically')

关于如何(合理)解决这个问题的任何建议？
总之，我们需要:

能够捕获最初引发的异常，并能够捕获 SpecialException

保留回溯以便于调试

包含原始异常的错误消息

我试过的:
尝试使用 raise SpecialException from e .虽然我们能够从最初引发的异常中查看错误消息和回溯，但我们不再能够通过最初抛出的异常类型来捕获它... 例如:我们可以捕获 SpecialException ，但抓不到 ValueError :

def crashAndBurn():
    try:
        int('asdf') # ValueError
    except Exception as e:
        raise SpecialException('Special Exception Encountered').with_traceback(e.__traceback__) from e

try:
    crashAndBurn()
except ValueError as e:
    print('This will never be encountered')
except SpecialException as e:
    print('This will be encountered, when we wanted it to be handled above')

然而，我们在技术上获得的最接近的满足了我们的需求:

虽然引发的异常可以被捕获为 SpecialException或 ValueError ，它实际上是作为另一个一次性使用类提出的:DynamicSpecialException

这真的很恶心，而且看起来非常不 Pythonic

def crashAndBurn():
    try:
        int('asdf') # ValueError
    except Exception as e:
        class DynamicSpecialException(SpecialException, e.__class__):
            pass # I feel dirty
        raise DynamicSpecialException('Special Exception Encountered').with_traceback(e.__traceback__)

try:
    crashAndBurn()
except ValueError as e:
    print('Caught as a ValueError!')

try:
    crashAndBurn()
except SpecialException as e:
    print('Caught as SpecialException!')

我真正期待找到的是类似于 raise e.extend(SpecialException) 的东西。或 raise SpecialException.from(e) - 而不是这个兔子洞，我今天似乎摆动了下来! :)

Answer 1

这里有点小题大做。它似乎可以完成您想要的大部分工作，只是它附加了特殊工厂处理的堆栈跟踪。
我学到的是你不能交换异常类，e.__class__ = <dynamic class> ，您必须创建一个新的并提高它。

import pdb
from traceback import print_exc as xp
import sys

def cpdb():
    """ put `pdb` on commmand line to halt execution in debugger """
    return "pdb" in sys.argv



class SpecialException(Exception):

    def solve_world_hunger(self):
        print(f"eat more 🦄")

def specialfactory(e):
    """ creates a class dynamically and keeps the original as a base"""
    cls_ = type("SpecialException", (SpecialException, e.__class__),{})
    e2 = cls_(str(e))
    e2.ori = e
    e2.__dict__.update(**e.__dict__)

    # 👇 you can try different flavors to see what changes:
    #  basically, I haven't found a way to suppress `The above exception was the direct cause of the following exception:`
    #  see also https://stackoverflow.com/questions/33809864/disable-exception-chaining-in-python-3

    # return e2
    # raise e2.        raise specialfactory(e).with_traceback(e.__traceback__) from e
    # raise e2 from e
    raise e2.with_traceback(e.__traceback__) from e


def crashAndBurn(no_special=False, custom_message=None):
    try:

        if custom_message:
            exc = ValueError(custom_message)
            exc.foo = "bar"
            raise exc

        int('asdf') # ValueError
    except Exception as e:
        if no_special:
            #just to investigate what things look like for a plain ValueError
            raise
        # raise specialfactory(e).with_traceback(e.__traceback__) from e
        raise specialfactory(e) from e



#################################################################
# check what a regular unchanged ValueError looks like
#################################################################

try:
    print("\n\n\n🔬regular ValueError, unchanged")
    crashAndBurn(no_special=1)
except ValueError as e:
    if cpdb(): pdb.set_trace()
    print(f'  plain ValueError: {e}')
    xp()
except SpecialException as e:
    if cpdb(): pdb.set_trace()
    print(f'  Caught as a SpecialException!: {e}')
    xp()

#################################################################
# catch a Special as a ValueError
#################################################################


try:
    print("\n\n\n🔬ValueError ")
    crashAndBurn()
except ValueError as e:
    if cpdb(): pdb.set_trace()
    print(f'  Caught as a ValueError! {e}')
    xp()
except SpecialException as e:
    if cpdb(): pdb.set_trace()
    print(f' Caught as a SpecialException! {e}')
    xp()

#################################################################
# catch a Special 
#################################################################



try:
    print("\n\n\n🔬SpecialException handling")
    crashAndBurn()
except SpecialException as e:
    if cpdb(): pdb.set_trace()
    print(f'  Caught as a SpecialException! {e} {e.solve_world_hunger()}')
    xp()
except ValueError as e:
    if cpdb(): pdb.set_trace()
    print(f'  Caught as a ValueError! {e}')
    xp()

#################################################################
# custom variables are still available
#################################################################

try:
    print("\n\n\n🔬ValueError with custom_message/content ")
    crashAndBurn(custom_message="my custom_message")
except SpecialException as e:
    if cpdb(): pdb.set_trace()
    print(f'  Caught as a SpecialException! {e} {e.foo=} {e.solve_world_hunger()}')
    xp()
except ValueError as e:
    if cpdb(): pdb.set_trace()
    print(f'  Caught as a ValueError! {e}')
    xp()

输出:

Traceback (most recent call last):
  File "test_183.py", line 57, in <module>
    crashAndBurn(no_special=1)
  File "test_183.py", line 41, in crashAndBurn
    int('asdf') # ValueError
ValueError: invalid literal for int() with base 10: 'asdf'
Traceback (most recent call last):
  File "test_183.py", line 41, in crashAndBurn
    int('asdf') # ValueError
ValueError: invalid literal for int() with base 10: 'asdf'

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

Traceback (most recent call last):
  File "test_183.py", line 74, in <module>
    crashAndBurn()
  File "test_183.py", line 47, in crashAndBurn
    raise specialfactory(e) from e
  File "test_183.py", line 30, in specialfactory
    raise e2.with_traceback(e.__traceback__) from e
  File "test_183.py", line 41, in crashAndBurn
    int('asdf') # ValueError
SpecialException: invalid literal for int() with base 10: 'asdf'
Traceback (most recent call last):
  File "test_183.py", line 41, in crashAndBurn
    int('asdf') # ValueError
ValueError: invalid literal for int() with base 10: 'asdf'

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

Traceback (most recent call last):
  File "test_183.py", line 92, in <module>
    crashAndBurn()
  File "test_183.py", line 47, in crashAndBurn
    raise specialfactory(e) from e
  File "test_183.py", line 30, in specialfactory
    raise e2.with_traceback(e.__traceback__) from e
  File "test_183.py", line 41, in crashAndBurn
    int('asdf') # ValueError
SpecialException: invalid literal for int() with base 10: 'asdf'
Traceback (most recent call last):
  File "test_183.py", line 39, in crashAndBurn
    raise exc
ValueError: my custom_message

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

Traceback (most recent call last):
  File "test_183.py", line 108, in <module>
    crashAndBurn(custom_message="my custom_message")
  File "test_183.py", line 47, in crashAndBurn
    raise specialfactory(e) from e
  File "test_183.py", line 30, in specialfactory
    raise e2.with_traceback(e.__traceback__) from e
  File "test_183.py", line 39, in crashAndBurn
    raise exc
SpecialException: my custom_message



🔬regular ValueError, unchanged
  plain ValueError: invalid literal for int() with base 10: 'asdf'



🔬ValueError 
  Caught as a ValueError! invalid literal for int() with base 10: 'asdf'



🔬SpecialException handling
eat more 🦄
  Caught as a SpecialException! invalid literal for int() with base 10: 'asdf' None



🔬ValueError with custom_message/content 
eat more 🦄
  Caught as a SpecialException! my custom_message e.foo='bar' None