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:
SpecialException
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:SpecialException
或 ValueError
,它实际上是作为另一个一次性使用类提出的:DynamicSpecialException
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! :)
最佳答案
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
关于python - 在 Python 中使用自定义异常动态扩展异常?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/64218275/