python multiprocessing on windows, if __name__ == "__main__"

Question

Running python 2.7 on windows 7 (64bit). When reading the docs for library module `multiprocessing`, it states several times the importance of the `__main__` module, including the conditional (especially in Windows): ``` if __name__ == "__main__": # create Process() here ``` My understanding, is that you don't want to create Process() instances in the global namespace of the module (because when the child process imports the module, he will spawn yet another inadvertently). I do not have to place Process managers at the very top level of my package execution hierarchy though (execution in the PARENT). As long as my Process()'s are created, managed, and terminated in a class method, or even in a function closure. Just not in the toplevel module namespace. Am I understanding this warning/requirement correctly? EDIT After the first two responses, I add this quotation. This is in the introduction for Section 16.6 multiprocessing from the 2.7 docs. Note: Functionality within this package r…

Accepted Answer

You do not have to call `Process()` from the "top level" of the module. It is perfectly fine to call `Process` from a class method.

The only caveat is that you can not allow `Process()` to be called if or when the module is imported.

Since Windows has no `fork`, the multiprocessing module starts a new Python process and imports the calling module. If `Process()` gets called upon import, then this sets off an infinite succession of new processes (or until your machine runs out of resources). This is the reason for hiding calls to `Process()` inside

```
if __name__ == "__main__"
```

since statements inside this `if-statement` will not get called upon import.

python multiprocessing on windows, if name == "main"

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