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Henry SchreinerandRalf W. Grosse-Kunstleve 63d627c574 feat!: drop support for Python 3.8, MSVC 2017 (#6110) 
* feat!: drop support for Python 3.8

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

* ci(appveyor): use Python 3.9

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

* feat!: require MSVC 2019 or newer

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

* fix(appveyor): build against the Python that has the test packages

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

* fix(appveyor): give the linker Python's libs directory

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

* fix(appveyor): link the release Python library in Debug

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

* chore(appveyor): print link settings to debug LNK1104

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

* fix(appveyor): take the release Python library in Debug

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

* chore(appveyor): drop the temporary link diagnostic

Assisted-by: ClaudeCode:claude-opus-5

* fix(tests): guard the unraisable warning filter for pytest < 6

The distro pytest in the Clang and GCC Docker jobs has no
PytestUnraisableExceptionWarning, so an unconditional filterwarnings
mark makes pytest fail with an INTERNALERROR after the tests pass.

Assisted-by: ClaudeCode:claude-opus-5

Claude-Session: https://claude.ai/code/session_01Aimf6HuSz1vLRwBnbxmCTc

* docs: address review items on version hints, embed docs, and a PyPy xfail

Extend Python_ADDITIONAL_VERSIONS through 3.15, describe the PyConfig
behavior of initialize_interpreter, and drop the stale Python 3.8 wording
from the PyPy xfail reason.

Assisted-by: ClaudeCode:claude-opus-5

* Update README.rst

Co-authored-by: Ralf W. Grosse-Kunstleve <rwgkio@gmail.com>

---------

Co-authored-by: Ralf W. Grosse-Kunstleve <rwgkio@gmail.com>
2026-07-31 22:04:32 -07:00

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.. figure:: https://github.com/pybind/pybind11/raw/master/docs/pybind11-logo.png
:alt: pybind11 logo
**pybind11 (v3) — Seamless interoperability between C++ and Python**
|Latest Documentation Status| |Stable Documentation Status| |Gitter chat| |GitHub Discussions|
|CI| |Build status| |SPEC 4 — Using and Creating Nightly Wheels|
|Repology| |PyPI package| |Conda-forge| |Python Versions|
`Setuptools example <https://github.com/pybind/python_example>`_
• `Scikit-build example <https://github.com/pybind/scikit_build_example>`_
• `CMake example <https://github.com/pybind/cmake_example>`_
.. start
**pybind11** is a lightweight header-only library that exposes C++ types
in Python and vice versa, mainly to create Python bindings of existing
C++ code. Its goals and syntax are similar to the excellent
`Boost.Python <http://www.boost.org/doc/libs/1_58_0/libs/python/doc/>`_
library by David Abrahams: to minimize boilerplate code in traditional
extension modules by inferring type information using compile-time
introspection.
The main issue with Boost.Python—and the reason for creating such a
similar project—is Boost. Boost is an enormously large and complex suite
of utility libraries that works with almost every C++ compiler in
existence. This compatibility has its cost: arcane template tricks and
workarounds are necessary to support the oldest and buggiest of compiler
specimens. Now that C++11-compatible compilers are widely available,
this heavy machinery has become an excessively large and unnecessary
dependency.
Think of this library as a tiny self-contained version of Boost.Python
with everything stripped away that isn't relevant for binding
generation. Without comments, the core header files only require ~4K
lines of code and depend on Python (CPython 3.9+, PyPy, or GraalPy) and the C++
standard library. This compact implementation was possible thanks to some C++11
language features (specifically: tuples, lambda functions and variadic
templates). Since its creation, this library has grown beyond Boost.Python in
many ways, leading to dramatically simpler binding code in many common
situations.
Tutorial and reference documentation is provided at
`pybind11.readthedocs.io <https://pybind11.readthedocs.io/en/latest>`_.
A PDF version of the manual is available
`here <https://pybind11.readthedocs.io/_/downloads/en/latest/pdf/>`_.
And the source code is always available at
`github.com/pybind/pybind11 <https://github.com/pybind/pybind11>`_.
Core features
-------------
pybind11 can map the following core C++ features to Python:
- Functions accepting and returning custom data structures per value,
reference, or pointer
- Instance methods and static methods
- Overloaded functions
- Instance attributes and static attributes
- Arbitrary exception types
- Enumerations
- Callbacks
- Iterators and ranges
- Custom operators
- Single and multiple inheritance
- STL data structures
- Smart pointers with reference counting like ``std::shared_ptr``
- Internal references with correct reference counting
- C++ classes with virtual (and pure virtual) methods can be extended
in Python
- Integrated NumPy support (NumPy 2 requires pybind11 2.12+)
Goodies
-------
In addition to the core functionality, pybind11 provides some extra
goodies:
- CPython 3.9+, PyPy3 7.3.17+, and GraalPy 24.1+ are supported with an
implementation-agnostic interface (see older versions for older CPython
and PyPy versions).
- It is possible to bind C++11 lambda functions with captured
variables. The lambda capture data is stored inside the resulting
Python function object.
- pybind11 uses C++11 move constructors and move assignment operators
whenever possible to efficiently transfer custom data types.
- It's easy to expose the internal storage of custom data types through
Pythons' buffer protocols. This is handy e.g. for fast conversion
between C++ matrix classes like Eigen and NumPy without expensive
copy operations.
- pybind11 can automatically vectorize functions so that they are
transparently applied to all entries of one or more NumPy array
arguments.
- Python's slice-based access and assignment operations can be
supported with just a few lines of code.
- Everything is contained in just a few header files; there is no need
to link against any additional libraries.
- Binaries are generally smaller by a factor of at least 2 compared to
equivalent bindings generated by Boost.Python. A recent pybind11
conversion of PyRosetta, an enormous Boost.Python binding project,
`reported <https://graylab.jhu.edu/Sergey/2016.RosettaCon/PyRosetta-4.pdf>`_
a binary size reduction of **5.4x** and compile time reduction by
**5.8x**.
- Function signatures are precomputed at compile time (using
``constexpr``), leading to smaller binaries.
- With little extra effort, C++ types can be pickled and unpickled
similar to regular Python objects.
Supported platforms & compilers
-------------------------------
pybind11 is exercised in continuous integration across a range of operating
systems, Python versions, C++ standards, and toolchains. For an up-to-date
view of the combinations we currently test, please see the
`pybind11 GitHub Actions <https://github.com/pybind/pybind11/actions?query=branch%3Amaster>`_
and `AppVeyor <https://ci.appveyor.com/project/wjakob/pybind11>`_ logs.
The test matrix naturally evolves over time as older platforms and compilers
fall out of use and new ones are added by the community. Closely related
versions of a tested compiler or platform will often work as well in practice,
but we cannot promise to validate every possible combination. If a
configuration you rely on is missing from the matrix or regresses, issues and
pull requests to extend coverage are very welcome. At the same time, we need
to balance the size of the test matrix with the available CI resources,
such as GitHub's limits on concurrent jobs under the free tier.
About
-----
This project was created by `Wenzel
Jakob <http://rgl.epfl.ch/people/wjakob>`_. Significant features and/or
improvements to the code were contributed by
Jonas Adler,
Lori A. Burns,
Sylvain Corlay,
Eric Cousineau,
Aaron Gokaslan,
Ralf Grosse-Kunstleve,
Trent Houliston,
Axel Huebl,
@hulucc,
Yannick Jadoul,
Sergey Lyskov,
Johan Mabille,
Tomasz Miąsko,
Dean Moldovan,
Ben Pritchard,
Jason Rhinelander,
Boris Schäling,
Pim Schellart,
Henry Schreiner,
Ivan Smirnov,
Dustin Spicuzza,
Boris Staletic,
Ethan Steinberg,
Patrick Stewart,
Ivor Wanders,
and
Xiaofei Wang.
We thank Google for a generous financial contribution to the continuous
integration infrastructure used by this project.
Contributing
~~~~~~~~~~~~
See the `contributing
guide <https://github.com/pybind/pybind11/blob/master/.github/CONTRIBUTING.md>`_
for information on building and contributing to pybind11.
License
~~~~~~~
pybind11 is provided under a BSD-style license that can be found in the
`LICENSE <https://github.com/pybind/pybind11/blob/master/LICENSE>`_
file. By using, distributing, or contributing to this project, you agree
to the terms and conditions of this license.
.. |Latest Documentation Status| image:: https://readthedocs.org/projects/pybind11/badge?version=latest
:target: http://pybind11.readthedocs.org/en/latest
.. |Stable Documentation Status| image:: https://img.shields.io/badge/docs-stable-blue.svg
:target: http://pybind11.readthedocs.org/en/stable
.. |Gitter chat| image:: https://img.shields.io/gitter/room/gitterHQ/gitter.svg
:target: https://gitter.im/pybind/Lobby
.. |CI| image:: https://github.com/pybind/pybind11/workflows/CI/badge.svg
:target: https://github.com/pybind/pybind11/actions
.. |Build status| image:: https://ci.appveyor.com/api/projects/status/riaj54pn4h08xy40?svg=true
:target: https://ci.appveyor.com/project/wjakob/pybind11
.. |PyPI package| image:: https://img.shields.io/pypi/v/pybind11.svg
:target: https://pypi.org/project/pybind11/
.. |Conda-forge| image:: https://img.shields.io/conda/vn/conda-forge/pybind11.svg
:target: https://github.com/conda-forge/pybind11-feedstock
.. |Repology| image:: https://repology.org/badge/latest-versions/python:pybind11.svg
:target: https://repology.org/project/python:pybind11/versions
.. |Python Versions| image:: https://img.shields.io/pypi/pyversions/pybind11.svg
:target: https://pypi.org/project/pybind11/
.. |GitHub Discussions| image:: https://img.shields.io/static/v1?label=Discussions&message=Ask&color=blue&logo=github
:target: https://github.com/pybind/pybind11/discussions
.. |SPEC 4 — Using and Creating Nightly Wheels| image:: https://img.shields.io/badge/SPEC-4-green?labelColor=%23004811&color=%235CA038
:target: https://scientific-python.org/specs/spec-0004/
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