Archipelago fails when not in a if __name__ == "__main__" block about pagmo2 HOT 8 CLOSED

I failed to mention that I am running pygmo 2.4 on Python 3.6.2 64-bit through Anaconda on Windows 10.

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Your code is valid and works in our installation.
Maybe you have some installation problems?
How did you install pygmo2?

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I am uncertain if it was prepackaged with my Anaconda install or if installed using conda install pygmo.
conda list shows
pygmo 2.4 np112py36_0 conda-forge

*Edit
According to https://docs.anaconda.com/anaconda/packages/pkg-docs#python-3-6 pygmo is not prepackaged with Anaconda, so install has been through conda install pygmo

*Edit 2
I have uninstalled Python and Anaconda. Installed Miniconda, updated via conda update --all and installed pygmo with conda install pygmo. The error is the same as before.

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@lsangild Can you try to put the last three lines in a main block? Something like this:

if __name__ == "__main__":
    prob = pg.problem(sphere_function(3))
    algo = pg.algorithm(pg.bee_colony(gen = 20, limit = 20))
    archi = pg.archipelago(n=1, algo=algo, prob=prob, pop_size=10)

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@bluescarni That worked!
Actually I only need to put the archipelago line in a main block.
Can you elaborate on the cause of the issue?

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@lsangild The first instantiation of an island/archipelago triggers the creation of a pool of processes that do the actual parallel optimisation work when you call evolve(). These processes need to import your script in order to "see" the definition of your problem, but if in the import phase of your script you are creating an archipelago then this recursively triggers the creation of another pool of processes, which again will try to import your script, triggering the creation of an archipelago, etc. etc.

See also the first two answers here:

https://stackoverflow.com/questions/20360686/compulsory-usage-of-if-name-main-in-windows-while-using-multiprocessi

For pygmo, it means in practice that you should not create islands/archipelagos as part of the module code (i.e., the code that gets executed upon importing the module).

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I renamed the issue for future references.
Can we close this?

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Thank you for your help 👍

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