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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](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.x, or PyPy2.7 >= 5.7) 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

[http://pybind11.readthedocs.org/en/master](http://pybind11.readthedocs.org/en/master).

A PDF version of the manual is available

[here](https://media.readthedocs.org/pdf/pybind11/master/pybind11.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.x, and PyPy (PyPy2.7 >= 5.7) 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 17 or newer (16 with pybind11 v2.0 and 15 with pybind11 v2.0 and a [workaround](https://github.com/pybind/pybind11/issues/276))

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.

### 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.