pybind11/README.md

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# pybind11 — Seamless operability between C++11 and Python

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**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][] 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.org][].  A PDF version of the manual is available
[here][docs-pdf].

## 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 (tested on 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][pyrosetta-report] 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 17 or newer (16 with pybind11 v2.0 and 15 with pybind11
   v2.0 and a [workaround][intel-15-workaround])
5. Cygwin/GCC (tested on 2.5.1)

## 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,
Trent Houliston,
Axel Huebl,
@hulucc,
Sergey Lyskov
Johan Mabille,
Tomasz Miąsko,
Dean Moldovan,
Ben Pritchard,
Jason Rhinelander,
Boris Schäling,
Pim Schellart,
Henry Schreiner,
Ivan Smirnov, and
Patrick Stewart.

### Contributing

See the [contributing guide][] for information on building and contributing to
pybind11.


### License

pybind11 is provided under a BSD-style license that can be found in the
[`LICENSE`][] file. By using, distributing, or contributing to this project,
you agree to the terms and conditions of this license.


[pybind11.readthedocs.org]: http://pybind11.readthedocs.org/en/master
[docs-pdf]: https://media.readthedocs.org/pdf/pybind11/master/pybind11.pdf
[Boost.Python]: http://www.boost.org/doc/libs/1_58_0/libs/python/doc/
[pyrosetta-report]: http://graylab.jhu.edu/RosettaCon2016/PyRosetta-4.pdf
[contributing guide]:  https://github.com/pybind/pybind11/blob/master/CONTRIBUTING.md
[`LICENSE`]: https://github.com/pybind/pybind11/blob/master/LICENSE
[intel-15-workaround]: https://github.com/pybind/pybind11/issues/276
updated CI links 2016-03-01 14:41:02 +00:00			`![pybind11 logo](https://github.com/pybind/pybind11/raw/master/docs/pybind11-logo.png)`
added logo 2015-08-04 11:59:51 +00:00
			`# pybind11 — Seamless operability between C++11 and Python`
Initial commit 2015-07-05 18:05:44 +00:00
stable documentation link in README.md 2016-12-12 22:24:21 +00:00			`[![Documentation Status](https://readthedocs.org/projects/pybind11/badge/?version=master)](http://pybind11.readthedocs.org/en/master/?badge=master)`
			`[![Documentation Status](https://readthedocs.org/projects/pybind11/badge/?version=stable)](http://pybind11.readthedocs.org/en/stable/?badge=stable)`
added link to gitter chat room 2016-12-29 18:15:17 +00:00			`[![Gitter chat](https://img.shields.io/gitter/room/gitterHQ/gitter.svg)](https://gitter.im/pybind/Lobby)`
ci: add GHA badge 2020-07-26 17:50:31 +00:00			`[![CI](https://github.com/pybind/pybind11/workflows/CI/badge.svg)](https://github.com/pybind/pybind11/actions)`
documentation updates (clarified cross-module dependencies, added contributors, improved CSS) 2016-03-06 12:37:22 +00:00			`[![Build status](https://ci.appveyor.com/api/projects/status/riaj54pn4h08xy40?svg=true)](https://ci.appveyor.com/project/wjakob/pybind11)`
Added configuration files for Travis CI integration 2015-10-11 14:29:35 +00:00
docs: move CONTRIBUTING (#2402) * docs: move CONTRIBUTING * docs: clarify PyPy promise 2020-08-20 19:42:07 +00:00			`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][] library by`
			`David Abrahams: to minimize boilerplate code in traditional extension modules`
			`by inferring type information using compile-time introspection.`
Initial commit 2015-07-05 18:05:44 +00:00
			`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`
do more work with classes from pytypes.h (especially for STL container casting) 2016-01-17 21:36:41 +00:00			`everything stripped away that isn't relevant for binding generation. Without`
updated LOC values in README.md and intro.rst 2016-12-26 12:26:17 +00:00			`comments, the core header files only require ~4K lines of code and depend on`
docs: move CONTRIBUTING (#2402) * docs: move CONTRIBUTING * docs: clarify PyPy promise 2020-08-20 19:42:07 +00:00			`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.`
took a stab at some documentation 2015-10-13 00:57:16 +00:00
			`Tutorial and reference documentation is provided at`
docs: move CONTRIBUTING (#2402) * docs: move CONTRIBUTING * docs: clarify PyPy promise 2020-08-20 19:42:07 +00:00			`[pybind11.readthedocs.org][]. A PDF version of the manual is available`
			`[here][docs-pdf].`
Initial commit 2015-07-05 18:05:44 +00:00
			`## Core features`
docs: move CONTRIBUTING (#2402) * docs: move CONTRIBUTING * docs: clarify PyPy promise 2020-08-20 19:42:07 +00:00			`pybind11 can map the following core C++ features to Python:`
Initial commit 2015-07-05 18:05:44 +00:00
			`- Functions accepting and returning custom data structures per value, reference, or pointer`
			`- Instance methods and static methods`
			`- Overloaded functions`
			`- Instance attributes and static attributes`
updated README and changelog 2016-07-11 21:39:39 +00:00			`- Arbitrary exception types`
Initial commit 2015-07-05 18:05:44 +00:00			`- Enumerations`
			`- Callbacks`
Multiple inheritance support 2016-09-11 11:00:40 +00:00			`- Iterators and ranges`
Initial commit 2015-07-05 18:05:44 +00:00			`- Custom operators`
Multiple inheritance support 2016-09-11 11:00:40 +00:00			`- Single and multiple inheritance`
Initial commit 2015-07-05 18:05:44 +00:00			`- STL data structures`
docs: move CONTRIBUTING (#2402) * docs: move CONTRIBUTING * docs: clarify PyPy promise 2020-08-20 19:42:07 +00:00			- Smart pointers with reference counting like `std::shared_ptr`
Initial commit 2015-07-05 18:05:44 +00:00			`- Internal references with correct reference counting`
support for overriding virtual functions 2015-10-01 14:46:03 +00:00			`- C++ classes with virtual (and pure virtual) methods can be extended in Python`
Initial commit 2015-07-05 18:05:44 +00:00
			`## Goodies`
			`In addition to the core functionality, pybind11 provides some extra goodies:`

docs: move CONTRIBUTING (#2402) * docs: move CONTRIBUTING * docs: clarify PyPy promise 2020-08-20 19:42:07 +00:00			`- Python 2.7, 3.5+, and PyPy (tested on 7.3) are supported with an implementation-agnostic`
			`interface.`
took a stab at some documentation 2015-10-13 00:57:16 +00:00
			`- It is possible to bind C++11 lambda functions with captured variables. The`
			`lambda capture data is stored inside the resulting Python function object.`

WIP: PyPy support (#527) This commit includes modifications that are needed to get pybind11 to work with PyPy. The full test suite compiles and runs except for a last few functions that are commented out (due to problems in PyPy that were reported on the PyPy bugtracker). Two somewhat intrusive changes were needed to make it possible: two new tags ``py::buffer_protocol()`` and ``py::metaclass()`` must now be specified to the ``class_`` constructor if the class uses the buffer protocol and/or requires a metaclass (e.g. for static properties). Note that this is only for the PyPy version based on Python 2.7 for now. When the PyPy 3.x has caught up in terms of cpyext compliance, a PyPy 3.x patch will follow. 2016-12-16 14:00:46 +00:00			`- pybind11 uses C++11 move constructors and move assignment operators whenever`
			`possible to efficiently transfer custom data types.`

Initial commit 2015-07-05 18:05:44 +00:00			`- 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.`

generate more compact binaries 2015-07-26 14:33:49 +00:00			`- pybind11 can automatically vectorize functions so that they are transparently`
			`applied to all entries of one or more NumPy array arguments.`

Initial commit 2015-07-05 18:05:44 +00:00			`- Python's slice-based access and assignment operations can be supported with`
			`just a few lines of code.`

README.md: Missing "is". 2015-12-04 22:51:42 +00:00			`- Everything is contained in just a few header files; there is no need to link`
minor doc update 2015-10-18 12:48:24 +00:00			`against any additional libraries.`
license note 2015-12-05 13:41:25 +00:00
mention pyrosetta stats 2016-08-19 07:32:58 +00:00			`- Binaries are generally smaller by a factor of at least 2 compared to`
			`equivalent bindings generated by Boost.Python. A recent pybind11 conversion`
..one more typo 2016-09-21 17:30:23 +00:00			`of PyRosetta, an enormous Boost.Python binding project,`
docs: move CONTRIBUTING (#2402) * docs: move CONTRIBUTING * docs: clarify PyPy promise 2020-08-20 19:42:07 +00:00			`[reported][pyrosetta-report] a binary size reduction of 5.4x and compile`
			`time reduction by 5.8x.`
Much more efficient generation of function signatures, updated docs This modification taps into some newer C++14 features (if present) to generate function signatures considerably more efficiently at compile time rather than at run time. With this change, pybind11 binaries are now 2.1 times smaller compared to the Boost.Python baseline in the benchmark. Compilation times get a nice improvement as well. Visual Studio 2015 unfortunately doesn't implement 'constexpr' well enough yet to support this change and uses a runtime fallback. 2016-01-17 21:36:36 +00:00
docs: move CONTRIBUTING (#2402) * docs: move CONTRIBUTING * docs: clarify PyPy promise 2020-08-20 19:42:07 +00:00			- Function signatures are precomputed at compile time (using `constexpr`),
Use semi-constexpr signatures on MSVC MSCV does not allow `&typeid(T)` in constexpr contexts, but the string part of the type signature can still be constexpr. In order to avoid `typeid` as long as possible, `descr` is modified to collect type information as template parameters instead of constexpr `typeid`. The actual `std::type_info` pointers are only collected in the end, as a `constexpr` (gcc/clang) or regular (MSVC) function call. Not only does it significantly reduce binary size on MSVC, gcc/clang benefit a little bit as well, since they can skip some intermediate `std::type_info*` arrays. 2017-07-02 10:52:00 +00:00			`leading to smaller binaries.`
Much more efficient generation of function signatures, updated docs This modification taps into some newer C++14 features (if present) to generate function signatures considerably more efficiently at compile time rather than at run time. With this change, pybind11 binaries are now 2.1 times smaller compared to the Boost.Python baseline in the benchmark. Compilation times get a nice improvement as well. Visual Studio 2015 unfortunately doesn't implement 'constexpr' well enough yet to support this change and uses a runtime fallback. 2016-01-17 21:36:36 +00:00
convenience wrapper for constructing iterators (fixes #142) 2016-04-13 21:33:00 +00:00			`- With little extra effort, C++ types can be pickled and unpickled similar to`
			`regular Python objects.`

added note about supported compiler versions 2016-02-20 20:00:45 +00:00			`## Supported compilers`

Added minimum compiler version assertions We now require (and enforce at compile time): - GCC 4.8+ - clang 3.3+ (5.0+ for Apple's renumbered clang) - MSVC 2015u3+ - ICC 15+ This also updates the versions listed in the README, and removes a now-redundant MSVC version check. 2017-03-14 14:38:22 +00:00			`1. Clang/LLVM 3.3 or newer (for Apple Xcode's clang, this is 5.0.0 or newer)`
Make non-ancient version of GCC explicit in documentation (it means 4.8+) (#575) 2016-12-28 11:10:11 +00:00			`2. GCC 4.8 or newer`
Added minimum compiler version assertions We now require (and enforce at compile time): - GCC 4.8+ - clang 3.3+ (5.0+ for Apple's renumbered clang) - MSVC 2015u3+ - ICC 15+ This also updates the versions listed in the README, and removes a now-redundant MSVC version check. 2017-03-14 14:38:22 +00:00			`3. Microsoft Visual Studio 2015 Update 3 or newer`
docs: move CONTRIBUTING (#2402) * docs: move CONTRIBUTING * docs: clarify PyPy promise 2020-08-20 19:42:07 +00:00			`4. Intel C++ compiler 17 or newer (16 with pybind11 v2.0 and 15 with pybind11`
			`v2.0 and a [workaround][intel-15-workaround])`
add tested Cygwin version to README.md 2016-06-02 18:31:17 +00:00			`5. Cygwin/GCC (tested on 2.5.1)`
added note about supported compiler versions 2016-02-20 20:00:45 +00:00
about statement 2016-03-01 11:45:08 +00:00			`## About`

WIP: PyPy support (#527) This commit includes modifications that are needed to get pybind11 to work with PyPy. The full test suite compiles and runs except for a last few functions that are commented out (due to problems in PyPy that were reported on the PyPy bugtracker). Two somewhat intrusive changes were needed to make it possible: two new tags ``py::buffer_protocol()`` and ``py::metaclass()`` must now be specified to the ``class_`` constructor if the class uses the buffer protocol and/or requires a metaclass (e.g. for static properties). Note that this is only for the PyPy version based on Python 2.7 for now. When the PyPy 3.x has caught up in terms of cpyext compliance, a PyPy 3.x patch will follow. 2016-12-16 14:00:46 +00:00			`This project was created by [Wenzel Jakob](http://rgl.epfl.ch/people/wjakob).`
about statement 2016-03-01 11:45:08 +00:00			`Significant features and/or improvements to the code were contributed by`
			`Jonas Adler,`
README.md: added several folks who've made repeated contributions 2019-06-12 19:10:37 +00:00			`Lori A. Burns,`
about statement 2016-03-01 11:45:08 +00:00			`Sylvain Corlay,`
contributor list update 2016-09-27 16:02:20 +00:00			`Trent Houliston,`
about statement 2016-03-01 11:45:08 +00:00			`Axel Huebl,`
Working type casters for wide strings and wide characters 2016-03-08 18:40:32 +00:00			`@hulucc,`
stl_bind redesign & cleanup pass 2016-05-15 18:50:38 +00:00			`Sergey Lyskov`
documentation updates (clarified cross-module dependencies, added contributors, improved CSS) 2016-03-06 12:37:22 +00:00			`Johan Mabille,`
updated contributors in README.md 2016-05-29 10:37:11 +00:00			`Tomasz Miąsko,`
			`Dean Moldovan,`
minor README.md fix 2016-07-12 14:58:55 +00:00			`Ben Pritchard,`
add Jason Rhinelander to contributors list 2016-08-11 22:58:49 +00:00			`Jason Rhinelander,`
Update changelog and authors 2016-08-13 20:17:26 +00:00			`Boris Schäling,`
added @patstew to README.md 2017-03-14 01:51:09 +00:00			`Pim Schellart,`
README.md: added several folks who've made repeated contributions 2019-06-12 19:10:37 +00:00			`Henry Schreiner,`
added @patstew to README.md 2017-03-14 01:51:09 +00:00			`Ivan Smirnov, and`
			`Patrick Stewart.`
about statement 2016-03-01 11:45:08 +00:00
docs: move CONTRIBUTING (#2402) * docs: move CONTRIBUTING * docs: clarify PyPy promise 2020-08-20 19:42:07 +00:00			`### Contributing`

			`See the [contributing guide][] for information on building and contributing to`
			`pybind11.`


license note 2015-12-05 13:41:25 +00:00			`### License`

			`pybind11 is provided under a BSD-style license that can be found in the`
docs: move CONTRIBUTING (#2402) * docs: move CONTRIBUTING * docs: clarify PyPy promise 2020-08-20 19:42:07 +00:00			[`LICENSE`][] file. By using, distributing, or contributing to this project,
license note 2015-12-05 13:41:25 +00:00			`you agree to the terms and conditions of this license.`
docs: move CONTRIBUTING (#2402) * docs: move CONTRIBUTING * docs: clarify PyPy promise 2020-08-20 19:42:07 +00:00

			`[pybind11.readthedocs.org]: http://pybind11.readthedocs.org/en/master`
			`[docs-pdf]: https://media.readthedocs.org/pdf/pybind11/master/pybind11.pdf`
			`[Boost.Python]: http://www.boost.org/doc/libs/1_58_0/libs/python/doc/`
			`[pyrosetta-report]: http://graylab.jhu.edu/RosettaCon2016/PyRosetta-4.pdf`
			`[contributing guide]: https://github.com/pybind/pybind11/blob/master/CONTRIBUTING.md`
			[`LICENSE`]: https://github.com/pybind/pybind11/blob/master/LICENSE
			`[intel-15-workaround]: https://github.com/pybind/pybind11/issues/276`