TypeError when using multiprocessing with a custom class in Python 3.9
I'm reviewing some code and I'm optimizing some code but I've been banging my head against this for hours... I've looked through the documentation and I'm still confused about I'm stuck on something that should probably be simple. I've been struggling with this for a few days now and could really use some help. I'm working with a `TypeError` when trying to use the `multiprocessing` library with a custom class in Python 3.9. The class I'm passing to the multiprocessing pool is defined as follows: ```python class MyClass: def __init__(self, value): self.value = value def double(self): return self.value * 2 ``` When I attempt to run the following code, I receive an behavior: ```python from multiprocessing import Pool if __name__ == '__main__': instance = MyClass(5) with Pool(processes=2) as pool: result = pool.map(lambda x: instance.double(), range(5)) print(result) ``` The behavior message states: `TypeError: need to pickle MyClass objects`. This scenario seems to be related to how Python’s multiprocessing handles object serialization. I’ve researched and found out that `multiprocessing` uses `pickle` to serialize objects, which has limitations on custom objects. I tried to fix the scenario by using a function instead of a lambda: ```python def worker_func(instance): return instance.double() ``` And then calling it like this: ```python result = pool.map(lambda _: worker_func(instance), range(5)) ``` However, I still run into the same `TypeError`. I'm aware that using `multiprocessing.Manager()` could potentially allow me to share state, but I'm not sure if that's the best practice here. What are the correct ways to handle this situation? Are there any best practices when using custom classes with `multiprocessing`, or should I consider alternative approaches? Any suggestions would be really appreciated! My development environment is Ubuntu. Any ideas what could be causing this? I recently upgraded to Python stable. Hoping someone can shed some light on this. This issue appeared after updating to Python 3.11. How would you solve this? I'm using Python LTS in this project.