pybind11 setup and examples

Posted on Edited on

Cmake settings

Discuss the setting in cmake only.

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find_package(PythonLibs 3.6)
find_package(PythonInterp 3.6)
include_directories(${PYTHON_INCLUDE_DIRS}) 


...

set(PYBIND11_DIR ${CMAKE_CURRENT_SOURCE_DIR}/external/pybind11)
add_subdirectory(${PYBIND11_DIR}/ pybind11)


...

target_link_libraries(example_embed pybind11::embed)
# use link lib pybind11::embed to embed a python interpreter in you c++ code.

# if want to generate wrapper
pybind11_add_module(example_wrapper MODULE main.cpp)
target_link_libraries(example_wrapper PRIVATE pybind11::module)
set_target_properties(example_wrapper PROPERTIES PREFIX "${PYTHON_MODULE_PREFIX}"
SUFFIX "${PYTHON_MODULE_EXTENSION}")
#


In order to use anaconda python interpreter, run cmake with argument
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-DPYTHON_EXECUTABLE:FILEPATH=/Users/john_smith/anaconda3/envs/env_name/bin/python -DPython3_LIBRARIES=/Users/john_smith/anaconda3/envs/lib/libpython3.7m.dylib

be sure to clear the makefiles before reload cmake project

Wrap a C++ function

Assume the setting above, in the main.cpp file

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#include <pybind11/pybind11.h>
#include <map>
#include <pybind11/eigen.h> # make sure eigen library is within you search path
PYBIND11_MODULE(example_wrapper, m) {
    m.doc() = R"pbdoc(
        Pybind11 gen example_wrapper 
        -----------------------

        .. currentmodule:: example_wrapper

        .. autosummary::
           :toctree: _generate

           add
           subtract
    )pbdoc";


    m.def("add_any", [](py::EigenDRef<Eigen::MatrixXd> x, int r, int c, double v) { x(r,c) += v; });
    # this function would take the input of numpy array and pass a reference to eigen C++ data, generally faster than using copy initialization like [](Eigen::MatrixXd x){...} but not always possible
}

an example setup.py file is provided below,

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import os
import re
import sys
import platform
import subprocess

from setuptools import setup, Extension
from setuptools.command.build_ext import build_ext
from distutils.version import LooseVersion


class CMakeExtension(Extension):
    def __init__(self, name, sourcedir=''):
        Extension.__init__(self, name, sources=[])
        self.sourcedir = os.path.abspath(sourcedir)


class CMakeBuild(build_ext):
    def run(self):
        try:
            out = subprocess.check_output(['cmake', '--version'])
        except OSError:
            raise RuntimeError("CMake must be installed to build the following extensions: " +
                               ", ".join(e.name for e in self.extensions))

        if platform.system() == "Windows":
            cmake_version = LooseVersion(re.search(r'version\s*([\d.]+)', out.decode()).group(1))
            if cmake_version < '3.1.0':
                raise RuntimeError("CMake >= 3.1.0 is required on Windows")

        for ext in self.extensions:
            self.build_extension(ext)

    def build_extension(self, ext):
        extdir = os.path.abspath(os.path.dirname(self.get_ext_fullpath(ext.name)))
        cmake_args = ['-DCMAKE_LIBRARY_OUTPUT_DIRECTORY=' + extdir,
                      '-DPYTHON_EXECUTABLE=' + sys.executable]

        cfg = 'Debug' if self.debug else 'Release'
        build_args = ['--config', cfg]

        if platform.system() == "Windows":
            cmake_args += ['-DCMAKE_LIBRARY_OUTPUT_DIRECTORY_{}={}'.format(cfg.upper(), extdir)]
            if sys.maxsize > 2**32:
                cmake_args += ['-A', 'x64']
            build_args += ['--', '/m']
        else:
            cmake_args += ['-DCMAKE_BUILD_TYPE=' + cfg]
            build_args += ['--', '-j2']

        env = os.environ.copy()
        env['CXXFLAGS'] = '{} -DVERSION_INFO=\\"{}\\"'.format(env.get('CXXFLAGS', ''),
                                                              self.distribution.get_version())
        if not os.path.exists(self.build_temp):
            os.makedirs(self.build_temp)
        subprocess.check_call(['cmake', ext.sourcedir] + cmake_args, cwd=self.build_temp, env=env)
        subprocess.check_call(['cmake', '--build', '.'] + build_args, cwd=self.build_temp)

setup(
    name='example_wrapper',
    version='0.0.1',
    author='John Smith',
    author_email='JSmith@gmail.com',
    description='A test project using pybind11 and CMake',
    long_description='',
    ext_modules=[CMakeExtension('example_wrapper')],
    cmdclass=dict(build_ext=CMakeBuild),
    zip_safe=False,
)


put it in you python binding source dir (example)
and a simple run of
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pip install ./example

would install the python module example_wrapper into your env.

Wrap a C++ class