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Seamless operability between C++11 and Python
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* Allow type_caster of std::reference_wrapper<T> to be the same as a native reference. Before, both std::reference_wrapper<T> and std::reference_wrapper<const T> would invoke cast_op<type>. This doesn't allow the type_caster<> specialization for T to distinguish reference_wrapper types from value types. After, the type_caster<> specialization invokes cast_op<type&>, which allows reference_wrapper to behave in the same way as a native reference type. * Add tests/examples for std::reference_wrapper<const T> * Add tests which use mutable/immutable variants This test is a chimera; it blends the pybind11 casters with a custom pytype implementation that supports immutable and mutable calls. In order to detect the immutable/mutable state, the cast_op needs to propagate it, even through e.g. std::reference<const T> Note: This is still a work in progress; some things are crashing, which likely means that I have a refcounting bug or something else missing. * Add/finish tests that distinguish const& from & Fixes the bugs in my custom python type implementation, demonstrate test that requires const& and reference_wrapper<const T> being treated differently from Non-const. * Add passing a const to non-const method. * Demonstrate non-const conversion of reference_wrapper in tests. Apply formatting presubmit check. * Fix build errors from presubmit checks. * Try and fix a few more CI errors * More CI fixes. * More CI fixups. * Try and get PyPy to work. * Additional minor fixups. Getting close to CI green. * More ci fixes? * fix clang-tidy warnings from presubmit * fix more clang-tidy warnings * minor comment and consistency cleanups * PyDECREF -> Py_DECREF * copy/move constructors * Resolve codereview comments * more review comment fixes * review comments: remove spurious & * Make the test fail even when the static_assert is commented out. This expands the test_freezable_type_caster a bit by: 1/ adding accessors .is_immutable and .addr to compare identity from python. 2/ Changing the default cast_op of the type_caster<> specialization to return a non-const value. In normal codepaths this is a reasonable default. 3/ adding roundtrip variants to exercise the by reference, by pointer and by reference_wrapper in all call paths. In conjunction with 2/, this demonstrates the failure case of the existing std::reference_wrpper conversion, which now loses const in a similar way that happens when using the default cast_op_type<>. * apply presubmit formatting * Revert inclusion of test_freezable_type_caster There's some concern that this test is a bit unwieldly because of the use of the raw <Python.h> functions. Removing for now. * Add a test that validates const references propagation. This test verifies that cast_op may be used to correctly detect const reference types when used with std::reference_wrapper. * mend * Review comments based changes. 1. std::add_lvalue_reference<type> -> type& 2. Simplify the test a little more; we're never returning the ConstRefCaster type so the class_ definition can be removed. * formatted files again. * Move const_ref_caster test to builtin_casters * Review comments: use cast_op and adjust some comments. * Simplify ConstRefCasted test I like this version better as it moves the assertion that matters back into python. |
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.. figure:: https://github.com/pybind/pybind11/raw/master/docs/pybind11-logo.png :alt: pybind11 logo **pybind11 — Seamless operability between C++11 and Python** |Latest Documentation Status| |Stable Documentation Status| |Gitter chat| |CI| |Build status| |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>`_ .. warning:: Combining older versions of pybind11 (< 2.6.0) with Python 3.9.0 will trigger undefined behavior that typically manifests as crashes during interpreter shutdown (but could also destroy your data. **You have been warned.**) We recommend that you update to the latest patch release of Python (3.9.1), which includes a `fix <https://github.com/python/cpython/pull/22670>`_ that resolves this problem. If you do use Python 3.9.0, please update to the latest version of pybind11 (2.6.0 or newer), which includes a temporary workaround specifically when Python 3.9.0 is detected at runtime. **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 (2.7 or 3.5+, or PyPy) and the C++ standard library. This compact implementation was possible thanks to some of the new 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 Goodies ------- In addition to the core functionality, pybind11 provides some extra goodies: - Python 2.7, 3.5+, and PyPy/PyPy3 7.3 are supported with an implementation-agnostic interface. - 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 <http://graylab.jhu.edu/RosettaCon2016/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 compilers ------------------- 1. Clang/LLVM 3.3 or newer (for Apple Xcode’s clang, this is 5.0.0 or newer) 2. GCC 4.8 or newer 3. Microsoft Visual Studio 2015 Update 3 or newer 4. Intel C++ compiler 18 or newer (`possible issue <https://github.com/pybind/pybind11/pull/2573>`_ on 20.2) 5. Cygwin/GCC (tested on 2.5.1) 6. NVCC (CUDA 11.0 tested) 7. NVIDIA PGI (20.7 and 20.9 tested) 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, 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, Boris Staletic, and Patrick Stewart. 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 :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 :target: https://pypi.org/project/pybind11/ .. |Conda-forge| image:: https://img.shields.io/conda/vn/conda-forge/pybind11 :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 :target: https://pypi.org/project/pybind11/