.. _compiling: Build systems ############# Building with setuptools ======================== For projects on PyPI, building with setuptools is the way to go. Sylvain Corlay has kindly provided an example project which shows how to set up everything, including automatic generation of documentation using Sphinx. Please refer to the [python_example]_ repository. .. [python_example] https://github.com/pybind/python_example Building with cppimport ======================== [cppimport]_ is a small Python import hook that determines whether there is a C++ source file whose name matches the requested module. If there is, the file is compiled as a Python extension using pybind11 and placed in the same folder as the C++ source file. Python is then able to find the module and load it. .. [cppimport] https://github.com/tbenthompson/cppimport .. _cmake: Building with CMake =================== For C++ codebases that have an existing CMake-based build system, a Python extension module can be created with just a few lines of code: .. code-block:: cmake cmake_minimum_required(VERSION 3.4...3.18) project(example LANGUAGES CXX) add_subdirectory(pybind11) pybind11_add_module(example example.cpp) This assumes that the pybind11 repository is located in a subdirectory named :file:`pybind11` and that the code is located in a file named :file:`example.cpp`. The CMake command ``add_subdirectory`` will import the pybind11 project which provides the ``pybind11_add_module`` function. It will take care of all the details needed to build a Python extension module on any platform. A working sample project, including a way to invoke CMake from :file:`setup.py` for PyPI integration, can be found in the [cmake_example]_ repository. .. [cmake_example] https://github.com/pybind/cmake_example .. versionchanged:: 2.6 CMake 3.4+ is required. pybind11_add_module ------------------- To ease the creation of Python extension modules, pybind11 provides a CMake function with the following signature: .. code-block:: cmake pybind11_add_module( [MODULE | SHARED] [EXCLUDE_FROM_ALL] [NO_EXTRAS] [THIN_LTO] [OPT_SIZE] source1 [source2 ...]) This function behaves very much like CMake's builtin ``add_library`` (in fact, it's a wrapper function around that command). It will add a library target called ```` to be built from the listed source files. In addition, it will take care of all the Python-specific compiler and linker flags as well as the OS- and Python-version-specific file extension. The produced target ```` can be further manipulated with regular CMake commands. ``MODULE`` or ``SHARED`` may be given to specify the type of library. If no type is given, ``MODULE`` is used by default which ensures the creation of a Python-exclusive module. Specifying ``SHARED`` will create a more traditional dynamic library which can also be linked from elsewhere. ``EXCLUDE_FROM_ALL`` removes this target from the default build (see CMake docs for details). Since pybind11 is a template library, ``pybind11_add_module`` adds compiler flags to ensure high quality code generation without bloat arising from long symbol names and duplication of code in different translation units. It sets default visibility to *hidden*, which is required for some pybind11 features and functionality when attempting to load multiple pybind11 modules compiled under different pybind11 versions. It also adds additional flags enabling LTO (Link Time Optimization) and strip unneeded symbols. See the :ref:`FAQ entry ` for a more detailed explanation. These latter optimizations are never applied in ``Debug`` mode. If ``NO_EXTRAS`` is given, they will always be disabled, even in ``Release`` mode. However, this will result in code bloat and is generally not recommended. As stated above, LTO is enabled by default. Some newer compilers also support different flavors of LTO such as `ThinLTO`_. Setting ``THIN_LTO`` will cause the function to prefer this flavor if available. The function falls back to regular LTO if ``-flto=thin`` is not available. If ``CMAKE_INTERPROCEDURAL_OPTIMIZATION`` is set (either ON or OFF), then that will be respected instead of the built-in flag search. The ``OPT_SIZE`` flag enables size-based optimization equivalent to the standard ``/Os`` or ``-Os`` compiler flags and the ``MinSizeRel`` build type, which avoid optimizations that that can substantially increase the size of the resulting binary. This flag is particularly useful in projects that are split into performance-critical parts and associated bindings. In this case, we can compile the project in release mode (and hence, optimize performance globally), and specify ``OPT_SIZE`` for the binding target, where size might be the main concern as performance is often less critical here. A ~25% size reduction has been observed in practice. This flag only changes the optimization behavior at a per-target level and takes precedence over the global CMake build type (``Release``, ``RelWithDebInfo``) except for ``Debug`` builds, where optimizations remain disabled. .. _ThinLTO: http://clang.llvm.org/docs/ThinLTO.html Configuration variables ----------------------- By default, pybind11 will compile modules with the compiler default or the minimum standard required by pybind11, whichever is higher. You can set the standard explicitly with `CMAKE_CXX_STANDARD `_: .. code-block:: cmake set(CMAKE_CXX_STANDARD 14) # or 11, 14, 17, 20 set(CMAKE_CXX_STANDARD_REQUIRED ON) # optional, ensure standard is supported set(CMAKE_CXX_EXTENSIONS OFF) # optional, keep compiler extensionsn off The variables can also be set when calling CMake from the command line using the ``-D=`` flag. You can also manually set ``CXX_STANDARD`` on a target or use ``target_compile_features`` on your targets - anything that CMake supports. Classic Python support: The target Python version can be selected by setting ``PYBIND11_PYTHON_VERSION`` or an exact Python installation can be specified with ``PYTHON_EXECUTABLE``. For example: .. code-block:: bash cmake -DPYBIND11_PYTHON_VERSION=3.6 .. # Another method: cmake -DPYTHON_EXECUTABLE=/path/to/python .. # This often is a good way to get the current Python, works in environments: cmake -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)") .. find_package vs. add_subdirectory --------------------------------- For CMake-based projects that don't include the pybind11 repository internally, an external installation can be detected through ``find_package(pybind11)``. See the `Config file`_ docstring for details of relevant CMake variables. .. code-block:: cmake cmake_minimum_required(VERSION 3.4...3.18) project(example LANGUAGES CXX) find_package(pybind11 REQUIRED) pybind11_add_module(example example.cpp) Note that ``find_package(pybind11)`` will only work correctly if pybind11 has been correctly installed on the system, e. g. after downloading or cloning the pybind11 repository : .. code-block:: bash # Classic CMake cd pybind11 mkdir build cd build cmake .. make install # CMake 3.15+ cd pybind11 cmake -S . -B build cmake --build build -j 2 # Build on 2 cores cmake --install build Once detected, the aforementioned ``pybind11_add_module`` can be employed as before. The function usage and configuration variables are identical no matter if pybind11 is added as a subdirectory or found as an installed package. You can refer to the same [cmake_example]_ repository for a full sample project -- just swap out ``add_subdirectory`` for ``find_package``. .. _Config file: https://github.com/pybind/pybind11/blob/master/tools/pybind11Config.cmake.in .. _find-python-mode: FindPython mode --------------- CMake 3.12+ (3.15+ recommended) added a new module called FindPython that had a highly improved search algorithm and modern targets and tools. If you use FindPython, pybind11 will detect this and use the existing targets instead: .. code-block:: cmake cmake_minumum_required(VERSION 3.15...3.18) project(example LANGUAGES CXX) find_package(Python COMPONENTS Interpreter Development REQUIRED) find_package(pybind11 CONFIG REQUIRED) # or add_subdirectory(pybind11) pybind11_add_module(example example.cpp) You can also use the targets (as listed below) with FindPython. If you define ``PYBIND11_FINDPYTHON``, pybind11 will perform the FindPython step for you (mostly useful when building pybind11's own tests, or as a way to change search algorithms from the CMake invocation, with ``-DPYBIND11_FINDPYTHON=ON``. .. warning:: If you use FindPython2 and FindPython3 to dual-target Python, use the individual targets listed below, and avoid targets that directly include Python parts. There are `many ways to hint or force a discovery of a specific Python installation `_), setting ``Python_ROOT_DIR`` may be the most common one (though with virtualenv/venv support, and Conda support, this tends to find the correct Python version more often than the old system did). .. versionadded:: 2.6 Advanced: interface library targets ----------------------------------- Pybind11 supports modern CMake usage patterns with a set of interface targets, available in all modes. The targets provided are: ``pybind11::headers`` Just the pybind11 headers and minimum compile requirements ``pybind11::python2_no_register`` Quiets the warning/error when mixing C++14 or higher and Python 2 ``pybind11::pybind11`` Python headers + ``pybind11::headers`` + ``pybind11::python2_no_register`` (Python 2 only) ``pybind11::python_link_helper`` Just the "linking" part of pybind11:module ``pybind11::module`` Everything for extension modules - ``pybind11::pybind11`` + ``Python::Module`` (FindPython CMake 3.15+) or ``pybind11::python_link_helper`` ``pybind11::embed`` Everything for embedding the Python interpreter - ``pybind11::pybind11`` + ``Python::Embed`` (FindPython) or Python libs ``pybind11::lto`` / ``pybind11::thin_lto`` An alternative to `INTERPROCEDURAL_OPTIMIZATION` for adding link-time optimization. ``pybind11::windows_extras`` ``/bigobj`` and ``/mp`` for MSVC. ``pybind11::opt_size`` ``/Os`` for MSVC, ``-Os`` for other compilers. Does nothing for debug builds. Two helper functions are also provided: ``pybind11_strip(target)`` Strips a target (uses ``CMAKE_STRIP`` after the target is built) ``pybind11_extension(target)`` Sets the correct extension (with SOABI) for a target. You can use these targets to build complex applications. For example, the ``add_python_module`` function is identical to: .. code-block:: cmake cmake_minimum_required(VERSION 3.4) project(example LANGUAGES CXX) find_package(pybind11 REQUIRED) # or add_subdirectory(pybind11) add_library(example MODULE main.cpp) target_link_libraries(example PRIVATE pybind11::module pybind11::lto pybind11::windows_extras) pybind11_extension(example) pybind11_strip(example) set_target_properties(example PROPERTIES CXX_VISIBILITY_PRESET "hidden" CUDA_VISIBILITY_PRESET "hidden") Instead of setting properties, you can set ``CMAKE_*`` variables to initialize these correctly. .. warning:: Since pybind11 is a metatemplate library, it is crucial that certain compiler flags are provided to ensure high quality code generation. In contrast to the ``pybind11_add_module()`` command, the CMake interface provides a *composable* set of targets to ensure that you retain flexibility. It can be expecially important to provide or set these properties; the :ref:`FAQ ` contains an explanation on why these are needed. .. versionadded:: 2.6 .. _nopython-mode: Advanced: NOPYTHON mode ----------------------- If you want complete control, you can set ``PYBIND11_NOPYTHON`` to completely disable Python integration (this also happens if you run ``FindPython2`` and ``FindPython3`` without running ``FindPython``). This gives you complete freedom to integrate into an existing system (like `Scikit-Build's `_ ``PythonExtensions``). ``pybind11_add_module`` and ``pybind11_extension`` will be unavailable, and the targets will be missing any Python specific behavior. .. versionadded:: 2.6 Embedding the Python interpreter -------------------------------- In addition to extension modules, pybind11 also supports embedding Python into a C++ executable or library. In CMake, simply link with the ``pybind11::embed`` target. It provides everything needed to get the interpreter running. The Python headers and libraries are attached to the target. Unlike ``pybind11::module``, there is no need to manually set any additional properties here. For more information about usage in C++, see :doc:`/advanced/embedding`. .. code-block:: cmake cmake_minimum_required(VERSION 3.4...3.18) project(example LANGUAGES CXX) find_package(pybind11 REQUIRED) # or add_subdirectory(pybind11) add_executable(example main.cpp) target_link_libraries(example PRIVATE pybind11::embed) .. _building_manually: Building manually ================= pybind11 is a header-only library, hence it is not necessary to link against any special libraries and there are no intermediate (magic) translation steps. On Linux, you can compile an example such as the one given in :ref:`simple_example` using the following command: .. code-block:: bash $ c++ -O3 -Wall -shared -std=c++11 -fPIC `python3 -m pybind11 --includes` example.cpp -o example`python3-config --extension-suffix` The flags given here assume that you're using Python 3. For Python 2, just change the executable appropriately (to ``python`` or ``python2``). The ``python3 -m pybind11 --includes`` command fetches the include paths for both pybind11 and Python headers. This assumes that pybind11 has been installed using ``pip`` or ``conda``. If it hasn't, you can also manually specify ``-I /include`` together with the Python includes path ``python3-config --includes``. Note that Python 2.7 modules don't use a special suffix, so you should simply use ``example.so`` instead of ``example`python3-config --extension-suffix```. Besides, the ``--extension-suffix`` option may or may not be available, depending on the distribution; in the latter case, the module extension can be manually set to ``.so``. On Mac OS: the build command is almost the same but it also requires passing the ``-undefined dynamic_lookup`` flag so as to ignore missing symbols when building the module: .. code-block:: bash $ c++ -O3 -Wall -shared -std=c++11 -undefined dynamic_lookup `python3 -m pybind11 --includes` example.cpp -o example`python3-config --extension-suffix` In general, it is advisable to include several additional build parameters that can considerably reduce the size of the created binary. Refer to section :ref:`cmake` for a detailed example of a suitable cross-platform CMake-based build system that works on all platforms including Windows. .. note:: On Linux and macOS, it's better to (intentionally) not link against ``libpython``. The symbols will be resolved when the extension library is loaded into a Python binary. This is preferable because you might have several different installations of a given Python version (e.g. the system-provided Python, and one that ships with a piece of commercial software). In this way, the plugin will work with both versions, instead of possibly importing a second Python library into a process that already contains one (which will lead to a segfault). Building with vcpkg =================== You can download and install pybind11 using the Microsoft `vcpkg `_ dependency manager: .. code-block:: bash git clone https://github.com/Microsoft/vcpkg.git cd vcpkg ./bootstrap-vcpkg.sh ./vcpkg integrate install vcpkg install pybind11 The pybind11 port in vcpkg is kept up to date by Microsoft team members and community contributors. If the version is out of date, please `create an issue or pull request `_ on the vcpkg repository. Generating binding code automatically ===================================== The ``Binder`` project is a tool for automatic generation of pybind11 binding code by introspecting existing C++ codebases using LLVM/Clang. See the [binder]_ documentation for details. .. [binder] http://cppbinder.readthedocs.io/en/latest/about.html [AutoWIG]_ is a Python library that wraps automatically compiled libraries into high-level languages. It parses C++ code using LLVM/Clang technologies and generates the wrappers using the Mako templating engine. The approach is automatic, extensible, and applies to very complex C++ libraries, composed of thousands of classes or incorporating modern meta-programming constructs. .. [AutoWIG] https://github.com/StatisKit/AutoWIG [robotpy-build]_ is a is a pure python, cross platform build tool that aims to simplify creation of python wheels for pybind11 projects, and provide cross-project dependency management. Additionally, it is able to autogenerate customizable pybind11-based wrappers by parsing C++ header files. .. [robotpy-build] https://robotpy-build.readthedocs.io