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REPL: AttributeError: module __mp_main__ has no attribute is_prime in ProcessPoolExecutor example #132898
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Question: did this occur because you hit Ctrl+C or killed the process somehow?Nevermind, it occurred on Linux as well with just running the example.
- changed the title
[-]A process in the process pool was terminated abruptly while the future was running or pending[/-][+]AttributeError: module `__mp_main__` has no attribute `is_prime` in `ProcessPoolExecutor` example[/+]on Apr 25, 2025 - changed the title
[-]AttributeError: module `__mp_main__` has no attribute `is_prime` in `ProcessPoolExecutor` example[/-][+]REPL: AttributeError: module `__mp_main__` has no attribute `is_prime` in `ProcessPoolExecutor` example[/+]on Apr 25, 2025 Ok, I only found the issue when the above code is being tested inside the REPL and not as a script (namely
python test.pyshould work but not when I C/C the above code). The best fix for now would be to just indicate in the docs "run it as a standalone script, not inside the REPL", but I don't know the exact reason why (well I can guess: it has something with pickling and probably globals that are not made available because they are only available in the REPL andProcessPoolExecutoris not able to find the correct "main" module).@wenming21 Your latest edit indicates that the error also occurs when running the example as a standalone script. What is the full traceback? (namely, what's above the "Traceback (most recent call last):"? because I do have other stuff written when I encounter the bug)
Why was this closed? @wenming21
I can also add that this only occurs on the main branch, on 3.13 it works fine.
3.14 has seen changes with the default start method so this could be the cause by the way (at least on Linux)
Reacted by Stan UlbrychWhat's happen when you change the
start_method?
I am on Mac, with a 3.12.8 version and I ran that script:
/bin/python3 -i /Users/yves/Desktop/Bugs/gh-132898.pyand in REPL, I callmain(), I have got errors:Ouptput
multiprocessing.get_start_method() = 'spawn' # I print the current `start_method` and keep only two numbers to check 112272535095293 is prime: True 1099726899285419 is prime: False >>> main() Process SpawnProcess-4: Traceback (most recent call last): File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/multiprocessing/process.py", line 314, in _bootstrap self.run() File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/multiprocessing/process.py", line 108, in run self._target(*self._args, **self._kwargs) File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/concurrent/futures/process.py", line 252, in _process_worker call_item = call_queue.get(block=True) ^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/multiprocessing/queues.py", line 122, in get return _ForkingPickler.loads(res) ^^^^^^^^^^^^^^^^^^^^^^^^^^ AttributeError: Can't get attribute 'is_prime' on <module '__main__' (<class '_frozen_importlib.BuiltinImporter'>)> Process SpawnProcess-3: Traceback (most recent call last): File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/multiprocessing/process.py", line 314, in _bootstrap self.run() File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/multiprocessing/process.py", line 108, in run self._target(*self._args, **self._kwargs) File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/concurrent/futures/process.py", line 252, in _process_worker call_item = call_queue.get(block=True) ^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/multiprocessing/queues.py", line 122, in get return _ForkingPickler.loads(res) ^^^^^^^^^^^^^^^^^^^^^^^^^^ AttributeError: Can't get attribute 'is_prime' on <module '__main__' (<class '_frozen_importlib.BuiltinImporter'>)> Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/Users/yves/Desktop/Bugs/gh-132898.py", line 31, in main for number, prime in zip(PRIMES, executor.map(is_prime, PRIMES)): ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/concurrent/futures/process.py", line 636, in _chain_from_iterable_of_lists for element in iterable: ^^^^^^^^ File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/concurrent/futures/_base.py", line 619, in result_iterator yield _result_or_cancel(fs.pop()) ^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/concurrent/futures/_base.py", line 317, in _result_or_cancel return fut.result(timeout) ^^^^^^^^^^^^^^^^^^^ File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/concurrent/futures/_base.py", line 456, in result return self.__get_result() ^^^^^^^^^^^^^^^^^^^ File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/concurrent/futures/_base.py", line 401, in __get_result raise self._exception concurrent.futures.process.BrokenProcessPool: A process in the process pool was terminated abruptly while
if I changed the
start_methodtoforkserver, I have got the same errors.And finally if the start method is
forkeverything is fine.
/usr/local/bin/python3 -i /Users/yves/Desktop/Bugs/gh-132898.pymultiprocessing.get_start_method() = 'fork' 112272535095293 is prime: True 1099726899285419 is prime: False >>> main() 112272535095293 is prime: True 1099726899285419 is prime: False >>>IMO, this issue is also causing by
start_methodbut I don't figure out how REPL is involved.
And a last remark, if you replace theis_primefunction withmath.sqrt, the script succeeds in anystart_methodcase .27 remaining items
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Bug report
Bug description:
python version:3.12.9
An error occurred when running as a standalone script.
An error message is reported when running the sample code of the python document:
Traceback (most recent call last):
File "C:\Users\wen\Desktop\test.py", line 32, in
main()
File "C:\Users\wen\Desktop\test.py", line 28, in main
for number, prime in zip(PRIMES, executor.map(is_prime, PRIMES)):
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Miniconda3\Lib\concurrent\futures\process.py", line 636, in _chain_from_iterable_of_lists
for element in iterable:
^^^^^^^^
File "C:\Miniconda3\Lib\concurrent\futures_base.py", line 619, in result_iterator
yield _result_or_cancel(fs.pop())
^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Miniconda3\Lib\concurrent\futures_base.py", line 317, in _result_or_cancel
return fut.result(timeout)
^^^^^^^^^^^^^^^^^^^
File "C:\Miniconda3\Lib\concurrent\futures_base.py", line 456, in result
return self.__get_result()
^^^^^^^^^^^^^^^^^^^
File "C:\Miniconda3\Lib\concurrent\futures_base.py", line 401, in __get_result
raise self._exception
concurrent.futures.process.BrokenProcessPool: A process in the process pool was terminated abruptly while the future was running or pending.
CPython versions tested on:
3.12
Operating systems tested on:
Windows 10
Linked PRs
multiprocessing.Processdocs about creating a process in a REPL session #137118multiprocessing.Processdocs about creating a process in a REPL (GH-137118) #137154multiprocessing.Processdocs about creating a process in a REPL (GH-137118) #137155