C/C++ 工程提供 Python 接口，有利于融合进 Python 的生态。现在 Python 在应用层，有其得天独厚的优势。尤其因为人工智能和大数据的推波助澜， Python 现在以及未来，将长期是最流行的语言之一。

那 C/C++ 怎么提供 Python 接口呢？

• ctypes: C 与 Python 绑定， Python 内建模块
• Boost.Python: C++ 与 Python 绑定， Boost 模块
• pybind11: C++11 与 Python 绑定， 减去了旧 C++ 支持，更轻量化

本文将介绍 pybind11 的环境准备与入门使用。

pybind11: https://github.com/pybind/pybind11

环境准备

pybind11 是一个 header-only 的库，换句话说，只需要 C++ 项目里直接 include pybind11 的头文件就能使用。

这里则介绍如何于 CMake 里引入 pybind11 。而更多编译系统的介绍，可见官方文档 Build systems 。

获取 pybind11

可以 git submodule 添加子模块，最好固定为某个版本：

git submodule add https://github.com/pybind/pybind11.git third_party/pybind11-2.5.0cd third_party/pybind11-2.5.0/git checkout tags/v2.5.0

或者，直接获取源码，放进相应子目录即可。

添加进 CMake

CMakeLists.txt 里 add_subdirectory pybind11 的路径，再用其提供的 pybind11_add_module 就能创建 pybind11 的模块了。

cmake_minimum_required(VERSION 3.1)project(start-pybind11 VERSION 0.1.0 LANGUAGES C CXX)set(MY_PYBIND ${MY_CURR}/third_party/pybind11-2.5.0)add_subdirectory(${MY_PYBIND})pybind11_add_module(example_pb example_pb.cpp)

如果想在已有 C++ 动态库上扩展 pybind11 绑定，那么 target_link_libraries 链接该动态库就可以了。

target_link_libraries(example_pb PUBLIC example)

绑定一个函数

我们先实现一个 add 函数，

int add(int i, int j) { return i + j;}

为了简化工程，可以直接实现在 example_pb.cpp 里，

#include <pybind11/pybind11.h>namespace py = pybind11;int add(int i, int j) { return i + j;}PYBIND11_MODULE(example_pb, m) { m.doc() = "example_pb bindings"; m.def("add", &add, "A function which adds two numbers");}

之后，于 CMakeLists.txt 所在目录，执行 cmake 编译就完成了。

示例代码

• first_steps.h
• first_steps.cc
• first_steps_pb.cc

绑定一个类

我们先实现一个定时触发器的类。使用如下：

#include <iostream>#include "tick.h"int main(int argc, char const *argv[]) { (void)argc; (void)argv; Tick tick(500, 5000); tick.SetTickEvent([&tick](std::int64_t elapsed_ms) { std::cout << "elapsed: " << elapsed_ms << " ms" << std::endl; if (elapsed_ms >= 2000) { tick.Stop(); } }); tick.Start(); tick.WaitLifeOver(); return 0;}

运行结果：

$ ./_output/bin/cpp_thread_callback/tick_test
elapsed: 0 ms
elapsed: 500 ms
elapsed: 1000 ms
elapsed: 1500 ms
elapsed: 2000 ms

该类的声明如下：

using TickEvent = std::function<void(std::int64_t elapsed_ms)>;using TickRunCallback = std::function<void()>;class Tick { public: using clock = std::chrono::high_resolution_clock; Tick(std::int64_t tick_ms, std::int64_t life_ms = std::numeric_limits<std::int64_t>::max()); Tick(TickEvent tick_event, std::int64_t tick_ms, std::int64_t life_ms = std::numeric_limits<std::int64_t>::max(), TickRunCallback run_beg = nullptr, TickRunCallback run_end = nullptr); virtual ~Tick(); bool IsRunning() const; void Start(); void Stop(bool wait_life_over = false); const std::chrono::time_point<clock> &GetTimeStart() const; void SetTickEvent(TickEvent &&tick_event); void SetTickEvent(const TickEvent &tick_event); void SetRunBegCallback(TickRunCallback &&run_beg); void SetRunBegCallback(const TickRunCallback &run_beg); void SetRunEndCallback(TickRunCallback &&run_end); void SetRunEndCallback(const TickRunCallback &run_end); void WaitLifeOver(); protected: // ...};

然后， pybind11 绑定实现如下：

#include <pybind11/pybind11.h>#include <pybind11/chrono.h>#include <pybind11/functional.h>#include <memory>#include "cpp/cpp_thread_callback/tick.h"namespace py = pybind11;using namespace pybind11::literals; // NOLINTPYBIND11_MODULE(tick_pb, m) { m.doc() = "tick_pb bindings"; py::class_<Tick, std::shared_ptr<Tick>>(m, "Tick") .def(py::init<std::int64_t, std::int64_t>()) .def(py::init<TickEvent, std::int64_t, std::int64_t, TickRunCallback, TickRunCallback>()) .def_property_readonly("is_running", &Tick::IsRunning) .def("start", &Tick::Start) .def("stop", &Tick::Stop, "wait_life_over"_a = false) .def("get_time_start", &Tick::GetTimeStart) .def("set_tick_event", [](Tick &self, const TickEvent &tick_event) { self.SetTickEvent(tick_event); }) .def("set_run_beg_callback", [](Tick &self, const TickRunCallback &run_beg) { self.SetRunBegCallback(run_beg); }) .def("set_run_end_callback", [](Tick &self, const TickRunCallback &run_end) { self.SetRunEndCallback(run_end); }) .def("wait_life_over", &Tick::WaitLifeOver, py::call_guard<py::gil_scoped_release>());}

编译出动态库后，把路径添加进 PYTHONPATH：

export PYTHONPATH=<path>:$PYTHONPATH# 依赖其他动态库的话，把路径添加进 LIBRARY_PATH# Linuxexport LD_LIBRARY_PATH=<path>:$LD_LIBRARY_PATH# macOSexport DYLD_LIBRARY_PATH=<path>:$DYLD_LIBRARY_PATH

之后，就可以于 Python 里调用了：

#!/usr/bin/env python# -*- coding: utf-8 -*-# pylint: disable=missing-docstring, import-errorimport tick_pb as tickdef _main(): t = tick.Tick(lambda elapsed_ms: print(f"elapsed: {elapsed_ms} ms"), 500, 1000, lambda: print("run beg"), lambda: print("run end")) t.start() t.wait_life_over()if __name__ == "__main__": _main()

运行结果：

$ python src/pybind/cpp_thread_callback/tick_test.py
run beg
elapsed: 0 ms
elapsed: 500 ms
elapsed: 1000 ms
run end

示例代码

• tick.h
• tick.cc
• tick_test.cc
• tick_pb.cc
• tick_test.py

运行示例代码

获取代码，

git clone https://github.com/ikuokuo/start-pybind11.git# 获取子模块cd start-pybind11/git submodule update --init

编译安装，

# 依赖 cmakecd start-pybind11/make install

编译结果，

$ tree _install_install├── bin│ └── cpp_thread_callback│ └── tick_test└── lib ├── cpp_thread_callback │ ├── libtick.0.1.0.dylib │ ├── libtick.0.1.dylib -> libtick.0.1.0.dylib │ ├── libtick.dylib -> libtick.0.1.dylib │ ├── tick_pb.0.1.0.cpython-37m-darwin.so │ ├── tick_pb.0.1.cpython-37m-darwin.so -> tick_pb.0.1.0.cpython-37m-darwin.so │ └── tick_pb.cpython-37m-darwin.so -> tick_pb.0.1.cpython-37m-darwin.so └── first_steps ├── first_steps_pb.0.1.0.cpython-37m-darwin.so ├── first_steps_pb.0.1.cpython-37m-darwin.so -> first_steps_pb.0.1.0.cpython-37m-darwin.so ├── first_steps_pb.cpython-37m-darwin.so -> first_steps_pb.0.1.cpython-37m-darwin.so ├── libfirst_steps.0.1.0.dylib ├── libfirst_steps.0.1.dylib -> libfirst_steps.0.1.0.dylib └── libfirst_steps.dylib -> libfirst_steps.0.1.dylib5 directories, 13 files

添加路径，

$ source setup.bash first_steps cpp_thread_callbackDYLD_LIBRARY_PATH, PYTHONPATH+ /Users/John/Workspace/Self/ikuokuo/start-pybind11/_install/lib/first_steps+ /Users/John/Workspace/Self/ikuokuo/start-pybind11/_install/lib/cpp_thread_callback

运行示例，

$ python src/pybind/cpp_thread_callback/tick_test.pyrun begelapsed: 0 mselapsed: 500 mselapsed: 1000 msrun end

结语

Go coding!

总结

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