[issue34837] Multiprocessing.pool API Extension - Pass Data to Workers w/o Globals

[Terry J. Reedy]

New submission from Terry J. Reedy <tjreedy at udel.edu>:

Quoting the PR:

Proposing a new kwarg in the __init__() method of multiprocessing.Pool named expect_initret.

This kwarg defaults to False. When set to True, the return value of the initializer function is passed to the function we are applying (i.e. func in Pool.map(func, ls)), as a kwarg named initret.

This PR includes thorough test coverage, and provides backwards compatibility (at least in Python3.x).

See blog post
https://thelaziestprogrammer.com/python/multiprocessing-pool-expect-initret-proposal
for example use cases, as well as an initial defense for why this makes the multiprocessing.Pool API more approachable, to more Python end-users, and augments the library.

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nosy: +davin, pitrou, terry.reedy

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