How to fix Python multiprocessing PicklingError: Can’t pickle function error?

Sometimes, we want to fix Python multiprocessing PicklingError: Can’t pickle function error.

In this article, we’ll look at how to fix Python multiprocessing PicklingError: Can’t pickle function error.

How to fix Python multiprocessing PicklingError: Can’t pickle function error?

To fix Python multiprocessing PicklingError: Can’t pickle function error, we should only run pickle in top level functions.

For instance, we write

import multiprocessing as mp

# ...

def work(foo):
    foo.work()

if __name__ == '__main__':   
    pool = mp.Pool()
    pool.apply_async(work, args=(foo,))
    pool.close()
    pool.join()

to define the work top level function,

And then we call pool.apply_async with work and the args arguments to run work which runs foo.work, which runs the pickle code.

Conclusion

To fix Python multiprocessing PicklingError: Can’t pickle function error, we should only pickle top level functions.