Re-order variants to prioritize narrower types#31504
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story645 merged 1 commit intomatplotlib:mainfrom Apr 16, 2026
Merged
Re-order variants to prioritize narrower types#31504story645 merged 1 commit intomatplotlib:mainfrom
story645 merged 1 commit intomatplotlib:mainfrom
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As of pybind/pybind11#5879, pybind11 will convert Python `int` to C `float`/`double`. For `std::variant`, pybind11 will attempt to convert arguments in the order of the type. So if `double` occurs earlier in the variant, then `int`/`long` will never be produced. By putting `int`/`long` before `double`, pybind11 will attempt that conversion first and we'll continue to produce our deprecation warning correctly. Fixes matplotlib#31495
Member
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Can we add this to the coding guidelines? (it's 100% the type of thing I'd forget when reviewing new C++ code) |
tacaswell
approved these changes
Apr 16, 2026
Member
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Confirmed that this works for me. Once we have this version of pybind11 in CI it will be very start failing hard so I'm not super worried about documenting it. |
Member
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or, if it goes in anyone's docs it should be pybind11's. |
Member
Author
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Also, as a note, these variants should go away after branching 3.11 as they are deprecations to be removed in 3.12. So we hopefully would not have to worry about it for too long. |
Member
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Ah, am I being too excited about back-porting this to 3.10 as well then? |
Member
Author
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No, it should go to 3.10 as well; the deprecations started in 3.10. |
story645
approved these changes
Apr 16, 2026
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…504-on-v3.10.x Backport PR #31504 on branch v3.10.x (Re-order variants to prioritize narrower types)
This was referenced Apr 21, 2026
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PR summary
As of pybind/pybind11#5879, pybind11 will convert Python
intto Cfloat/double. Forstd::variant, pybind11 will attempt to convert arguments in the order of the type.So if
doubleoccurs earlier in the variant, thenint/longwill never be produced. By puttingint/longbeforedouble, pybind11 will attempt that conversion first and we'll continue to produce our deprecation warning correctly.Fixes #31495
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