feat!: drop support for Python 3.8, MSVC 2017#6110
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The minimum supported version is now Python 3.9. pybind11 v3.0 was the last release that supports Python 3.8. The deprecation note said that support goes away in 3.1. Remove the code paths that this makes dead: - the `_PyObject_Vectorcall` fallback in `cast.h` - the `frame->f_code` and `frame->f_back` fallbacks in `pytypes.h` - the `PyFrame_FastToLocals` path in `get_type_override` - the conditional `Py_VISIT(Py_TYPE(self))` in `tp_traverse` - `PYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX`, the pre-PyConfig interpreter init, and the `widen_chars` helpers in `embed.h` Assisted-by: ClaudeCode:claude-opus-5
The AppVeyor job set `PYTHON: 38`, which makes the path `C:\Python38`. The image gives Python 3.9.13 as `C:\Python39`. Assisted-by: ClaudeCode:claude-opus-5
Python 3.9 is the new minimum, so MSVC 2017 is no longer needed. Raise the compile-time floor to _MSC_VER 1920 and remove the workarounds that only applied below it: std::launder, fold expressions, weak_from_this, aligned new/delete, the C4100 warning helper, and the func_handle syntax error. AppVeyor now builds with Visual Studio 2019. Assisted-by: ClaudeCode:claude-opus-5
henryiii
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CMake 4 has no FindPythonLibs, so pybind11 uses FindPython. FindPython reads the registry before PATH and selected `C:\Python314-x64`, but the test packages go into the Python on PATH. Pass `Python_ROOT_DIR` to name the correct one. Also set `CMAKE_ARCH`. It was never set, so the architecture came from the generator. Visual Studio 2017 defaults to Win32, but Visual Studio 2019 defaults to x64, which made this x86 job build 64-bit code. Assisted-by: ClaudeCode:claude-opus-5
The build compiled but failed to link with LNK1104 on a bare `python39.lib`. That name comes from the `#pragma comment(lib, ...)` in pyconfig.h, so the linker needs the directory. CMake 4 has no FindPythonLibs, and FindPython does not add it for this Debug x86 build. Put it on LIB instead. The directory listing is temporary, to confirm the library is present. Assisted-by: ClaudeCode:claude-opus-5
The image ships python39_d.lib next to python39.lib, so FindPython picks the debug import library for a Debug build. pybind11 undefines _DEBUG around Python.h, so pyconfig.h asks for python39.lib instead and the link failed with LNK1104. Name the release library for the debug slot. Setting LIB does not work, because MSBuild replaces it from the toolset, and it would link both import libraries. Assisted-by: ClaudeCode:claude-opus-5
Revert the two attempted fixes. Neither changed the failure: setting LIB does not survive MSBuild, and naming the release library for Python_LIBRARY_DEBUG had no effect. Print the Python cache entries and the link settings of a generated project file instead, to see what the linker really gets. Temporary. Assisted-by: ClaudeCode:claude-opus-5
The generated project file linked C:\Python39\libs\python39_d.lib in the Debug configuration, because the image ships debug binaries next to the release ones. pybind11 undefines _DEBUG around Python.h, so pyconfig.h asks for python39.lib in a #pragma comment(lib), which nothing on the link line satisfies and no library directory holds. Map Debug to the release artifacts. Assisted-by: ClaudeCode:claude-opus-5
Assisted-by: ClaudeCode:claude-opus-5
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🤖 AI text below 🤖 Why AppVeyor failedThe job compiled, then failed to link every module: The AppVeyor image has pybind11 undefines This is new because the Visual Studio 2019 image has CMake 4.1, which has no The fixOne flag, so Debug uses the release artifacts of imported targets: AppVeyor is green: Debug links Follow-up, not in this PRThe same mismatch can hit users. An MSVC Debug build against a Python installation that has the optional debug binaries links |
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Now require 3.9+ and matching MSVC 2019+.
🤖 AI text below 🤖
Description
Python 3.8 is at end of life. The deprecation note in the docs said that support
goes away in 3.1. This PR removes it. The minimum is now Python 3.9.
Configuration and tooling:
requires-python, the classifiers, and the mypy and pylint versions move to 3.9python39-develC:\Python39in place ofC:\Python38#errorindetail/common.hrejects Python earlier than 3.9setup_helpers.pyuses built-in generics in place oftyping.Listandtyping.TupleDead code paths that this removes:
_PyObject_Vectorcallfallback incast.hframe->f_codeandframe->f_backfallbacks inpytypes.hPyFrame_FastToLocalspath inget_type_overridePy_VISIT(Py_TYPE(self))intp_traversePYBIND11_PYCONFIG_SUPPORT_PY_VERSION_HEX, the pre-PyConfig interpreter init, andthe
widen_charshelpers inembed.hThe
embed.hmacro had a default of0x03080000. Its legacy branch cannot run whenthe minimum is 3.9, so the macro and the branch are gone. Four interpreter test cases
were behind that macro. They now always run.
I also renamed the
Add program dir to path pre-PyConfigtest case toAdd program dir to path without PyConfig, because no pre-PyConfig path is left.Suggested changelog entry:
📚 Documentation preview 📚: https://pybind11--6110.org.readthedocs.build/