


Why Multiprocessing Example Gives AttributeError
In an attempt to delve into multiprocessing, an individual encountered an AttributeError while adapting the introductory example from the documentation:
<code class="python">from multiprocessing import Pool def f(x): return x*x if __name__ == '__main__': with Pool(5) as p: print(p.map(f, [1, 2, 3]))</code>
The error: "AttributeError: can't get attribute 'f' on
To resolve this issue, it's important to understand that multiprocessing.Pool has a peculiar design feature. As noted in Python issue #25053, Pool sometimes falters when working with objects not defined in imported modules. As a workaround, you can define your function in a separate file and import the module.
Here's an example:
defs.py:
<code class="python">def f(x): return x*x</code>
run.py:
<code class="python">from multiprocessing import Pool import defs if __name__ == '__main__': with Pool(5) as p: print(p.map(defs.f, [1, 2, 3]))</code>
This modification should resolve the AttributeError. However, it's worth noting that the given example in the documentation might not be the most suitable for beginners due to this potential issue.
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