ProcessPoolExecutor swallows falsy Exceptions · Issue #132063 · python/cpython · GitHub

Bug report

Bug description:

import sys
import concurrent.futures

class MyException(Exception):

    def __bool__(self):
        return False


def raiser():
    raise MyException("foo")

def main():
    with concurrent.futures.ProcessPoolExecutor() as p:
        print(p.submit(raiser).result())

if __name__ == "__main__":
    sys.exit(main())

This program prints None, but should fail and print a traceback

CPython versions tested on:

CPython main branch, 3.14, 3.13, 3.12, 3.11, 3.10, 3.9

Operating systems tested on:

Linux

Linked PRs

I think there is something wrong here in the __get_result(self) method of Future class:

cpython/Lib/concurrent/futures/_base.py

Lines 393 to 400 in 6ab4ace

    
           if self._exception: 
        
               try: 
        
                   raise self._exception 
        
               finally: 
        
                   # Break a reference cycle with the exception in self._exception 
        
                   self = None 
        
           else: 
        
               return self._result

The test should be: if self._exception is not None: because if self._exception calls the __bool__ method of exception.

Edit: same problem here on line 443

cpython/Lib/concurrent/futures/process.py

Lines 441 to 446 in 6ab4ace

    
           # work_item can be None if another process terminated (see above) 
        
           if work_item is not None: 
        
               if result_item.exception: 
        
                   work_item.future.set_exception(result_item.exception) 
        
               else: 
        
                   work_item.future.set_result(result_item.result)

The test should be: if self._exception is not None: because if self._exception calls the bool method of exception.

Well spotted. Indeed, this should be changed to is not None. More generally, are there other places in the stdlib (or in mp-related code) where we have this issue?

More generally, are there other places in the stdlib

I saw these tests this morning:

cpython/Lib/traceback.py

Line 1123 in 255eb37

if (e and e.__cause__ is not None
cpython/Lib/traceback.py

Line 1144 in 255eb37

if (e and e.__context__ is not None
cpython/Lib/traceback.py

Line 1159 in 255eb37

if e and isinstance(e, BaseExceptionGroup):

May I open a PR ?

Unless they can make a silly bug, I think it's fine to keep them. However, unless @graingert wants to work on the issue itself, you may first fix the __get_result method first.

It's mandatory to work on both files /Lib/concurrent/futures/process.py and /Lib/concurrent/futures/_base.pyto fix this issue.

This should fix the same issue with a ThreadPoolExcecutor.

Please feel free to work on this, thanks! Thomas Grainger

…

On Fri, 4 Apr 2025, 15:41 Duprat, ***@***.***> wrote: It's mandatory to work on both files /Lib/concurrent/futures/process.py *and* /Lib/concurrent/futures/_base.pyto fix this issue. This should fix the same issue with a ThreadPoolExcecutor. — Reply to this email directly, view it on GitHub <#132063 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AADFATAV3324MMPIVXQ7JYL2X2KZHAVCNFSM6AAAAAB2OBLA4OVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDONZYHEZTGMRQGE> . You are receiving this because you were mentioned.Message ID: ***@***.***> [image: YvesDup]*YvesDup* left a comment (python/cpython#132063) <#132063 (comment)> It's mandatory to work on both files /Lib/concurrent/futures/process.py *and* /Lib/concurrent/futures/_base.pyto fix this issue. This should fix the same issue with a ThreadPoolExcecutor. — Reply to this email directly, view it on GitHub <#132063 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AADFATAV3324MMPIVXQ7JYL2X2KZHAVCNFSM6AAAAAB2OBLA4OVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDONZYHEZTGMRQGE> . You are receiving this because you were mentioned.Message ID: ***@***.***>

gh-132063: ensure that `ProcessPoolExecutor` does not swallow falsey …

pythongh-132063: ensure that `ProcessPoolExecutor` does not swallow f…

[3.13] gh-132063: ensure that `ProcessPoolExecutor` does not swallow …

ProcessPoolExecutor swallows falsy Exceptions · Issue #132063 · python/cpython · GitHub

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ProcessPoolExecutor swallows falsy Exceptions #132063

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	if self._exception:
	try:
	raise self._exception
	finally:
	# Break a reference cycle with the exception in self._exception
	self = None
	else:
	return self._result

	# work_item can be None if another process terminated (see above)
	if work_item is not None:
	if result_item.exception:
	work_item.future.set_exception(result_item.exception)
	else:
	work_item.future.set_result(result_item.result)

ProcessPoolExecutor swallows falsy Exceptions · Issue #132063 · python/cpython · GitHub

Repository navigation

ProcessPoolExecutor swallows falsy Exceptions #132063

Description

Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

Linked PRs

Activity

YvesDup commented on Apr 4, 2025

picnixz commented on Apr 4, 2025

YvesDup commented on Apr 4, 2025

picnixz commented on Apr 4, 2025

YvesDup commented on Apr 4, 2025

graingert commented on Apr 4, 2025

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