C/C++ 工程提供 Python 介面,有利於融合進 Python 的生態。現在 Python 在應用層,有其得天獨厚的優勢。尤其因為人工智慧和大資料的推波助瀾, Python 現在以及未來,將長期是最流行的語言之一。
那 C/C++ 怎麼提供 Python 介面呢?
- ctypes: C 與 Python 繫結, Python 內建模組
- Boost.Python: C++ 與 Python 繫結, Boost 模組
- pybind11: C++11 與 Python 繫結, 減去了舊 C++ 支援,更輕量化
本文將介紹 pybind11 的環境準備與入門使用。
- pybind11: https://github.com/pybind/pybind11
環境準備
pybind11 是一個 header-only
的庫,換句話說,只需要 C++ 專案裡直接 include pybind11 的標頭檔案就能使用。
這裡則介紹如何於 CMake 裡引入 pybind11 。而更多編譯系統的介紹,可見官方文件 Build systems 。
獲取 pybind11
可以 git submodule
新增子模組,最好固定為某個版本:
git submodule add https://github.com/pybind/pybind11.git third_party/pybind11-2.5.0
cd third_party/pybind11-2.5.0/
git checkout tags/v2.5.0
或者,直接獲取原始碼,放進相應子目錄即可。
新增進 CMake
CMakeLists.txt
裡 add_subdirectory
pybind11 的路徑,再用其提供的 pybind11_add_module
就能建立 pybind11 的模組了。
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++ 動態庫上擴充套件 pybind11 繫結,那麼 target_link_libraries
連結該動態庫就可以了。
target_link_libraries(example_pb PUBLIC example)
繫結一個函式
我們先實現一個 add
函式,
int add(int i, int j) {
return i + j;
}
為了簡化工程,可以直接實現在 example_pb.cpp
裡,
#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");
}
之後,於 CMakeLists.txt
所在目錄,執行 cmake
編譯就完成了。
示例程式碼
繫結一個類
我們先實現一個定時觸發器的類。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;
}
執行結果:
$ ./_output/bin/cpp_thread_callback/tick_test
elapsed: 0 ms
elapsed: 500 ms
elapsed: 1000 ms
elapsed: 1500 ms
elapsed: 2000 ms
該類的宣告如下:
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:
// ...
};
然後, pybind11 繫結實現如下:
#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; // NOLINT
PYBIND11_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>());
}
編譯出動態庫後,把路徑新增進 PYTHONPATH
:
export PYTHONPATH=<path>:$PYTHONPATH
# 依賴其他動態庫的話,把路徑新增進 LIBRARY_PATH
# Linux
export LD_LIBRARY_PATH=<path>:$LD_LIBRARY_PATH
# macOS
export DYLD_LIBRARY_PATH=<path>:$DYLD_LIBRARY_PATH
之後,就可以於 Python 裡呼叫了:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
# pylint: disable=missing-docstring, import-error
import tick_pb as tick
def _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()
執行結果:
$ python src/pybind/cpp_thread_callback/tick_test.py
run beg
elapsed: 0 ms
elapsed: 500 ms
elapsed: 1000 ms
run end
示例程式碼
執行示例程式碼
獲取程式碼,
git clone https://github.com/ikuokuo/start-pybind11.git
# 獲取子模組
cd start-pybind11/
git submodule update --init
編譯安裝,
# 依賴 cmake
cd start-pybind11/
make install
編譯結果,
$ 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.dylib
5 directories, 13 files
新增路徑,
$ source setup.bash first_steps cpp_thread_callback
DYLD_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
執行示例,
$ python src/pybind/cpp_thread_callback/tick_test.py
run beg
elapsed: 0 ms
elapsed: 500 ms
elapsed: 1000 ms
run end
結語
Go coding!