gh-140814: Fix call order in multiprocessing example #144606
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Move set_start_method() before freeze_support() in the "Safe importing
of main module" example. freeze_support() internally accesses the start
method context, which causes a subsequent set_start_method() to raise
RuntimeError('context has already been set').
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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I'm proposing we fix freeze_support() to not have the side effect in #144608 instead. |
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Summary
Swaps the order of
set_start_method()andfreeze_support()in the "Safe importing of main module" example in the multiprocessing docs.freeze_support()internally callsget_start_method(), which sets_actual_contexton the default context (Lib/multiprocessing/context.py:240-244). A subsequentset_start_method('spawn')then raisesRuntimeError('context has already been set')because_actual_contextis no longerNone(context.py:249).Calling
set_start_method()first avoids this, sincefreeze_support()will then use the already-configured spawn context.Test plan
make -C Doc checkpassesmake -C Doc htmlpasses (no warnings)Lib/multiprocessing/context.pylines 144-150, 240-254🤖 Generated with Claude Code
📚 Documentation preview 📚: https://cpython-previews--144606.org.readthedocs.build/