用C扩展Python3

官方文档：

https://docs.python.org/3/extending/index.html

• 交叉编译到aarch64上面

以交叉编译到aarch64上面为例，下面是Extest.c的实现：

#include <Python.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define BUFSIZE 10

int fac(int n) {
    if (n < 2)
        return 1;
    return n * fac(n - 1);
}

static PyObject * Extest_fac(PyObject *self, PyObject *args) {
    int res;//计算结果值
    int num;//参数
    PyObject* retval;//返回值

    //i表示需要传递进来的参数类型为整型，如果是，就赋值给num，如果不是，返回NULL；
    res = PyArg_ParseTuple(args, "i", &num);
    if (!res) {
        //包装函数返回NULL，就会在Python调用中产生一个TypeError的异常
        return NULL;
    }
    res = fac(num);
    //需要把c中计算的结果转成python对象，i代表整数对象类型。
    retval = (PyObject *)Py_BuildValue("i", res);
    return retval;
}

char *reverse(char *s) {
    register char t;
    char *p = s;
    char *q = (s + (strlen(s) - 1));
    while (p < q) {
        t = *p;
        *p++ = *q;
        *q-- = t;
    }
    return s;
}

static PyObject *
Extest_reverse(PyObject *self, PyObject *args) {
    char *orignal;
    if (!(PyArg_ParseTuple(args, "s", &orignal))) {
        return NULL;
    }
    return (PyObject *)Py_BuildValue("s", reverse(orignal));
}

static PyObject *
Extest_doppel(PyObject *self, PyObject *args) {
    char *orignal;
    char *reversed;
    PyObject * retval;
    if (!(PyArg_ParseTuple(args, "s", &orignal))) {
        return NULL;
    }
    retval = (PyObject *)Py_BuildValue("ss", orignal, reversed=reverse(strdup(orignal)));
    free(reversed);
    return retval;
}

static PyMethodDef
ExtestMethods[] = {
    {"fac", Extest_fac, METH_VARARGS},
    {"doppel", Extest_doppel, METH_VARARGS},
    {"reverse", Extest_reverse, METH_VARARGS},
    {NULL, NULL},
};

static struct PyModuleDef ExtestModule = {
    PyModuleDef_HEAD_INIT,
    "Extest",
    NULL,
    -1,
    ExtestMethods
};

PyMODINIT_FUNC PyInit_Extest(void)
{
    return PyModule_Create(&ExtestModule);
}

采用手动编译， Makefile如下：

CFLAGS = -pthread -fno-strict-aliasing -g -O2 -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes
CFLAGS += -fPIC -I /home/pengdonglin/src/qemu/python_cross_compile/Python3/aarch64/include/python3.6m
CC = /home/pengdonglin/src/qemu/aarch64/gcc-linaro-aarch64-linux-gnu-4.9-2014.07_linux/bin/aarch64-linux-gnu-gcc

all:Extest.so

Extest.o: Extest.c
    $(CC) $(CFLAGS) -c $^ -o $@

Extest.so: Extest.o
    $(CC) -pthread -shared $^ -o $@
    cp $@ /home/pengdonglin/src/qemu/python_cross_compile/Python3/aarch64/lib/python3.6/site-packages/

clean:
    $(RM) *.o *.so

.PHONY: clean all

执行make命令，就会在当前目录下生成一个Extest.so文件，然后将其放到板子上面的/usr/lib/python3.6/site-packages/下面即可

测试：

[root@aarch64 root]# cp /mnt/Extest.so /usr/lib/python3.6/site-packages/
[root@aarch64 root]# python3
Python 3.6.0 (default, Mar 23 2017, 10:54:13) 
[GCC 4.9.1 20140529 (prerelease)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import Extest
>>> Extest.fac(4)
24
>>> Extest.reverse("pengdonglin")
'nilgnodgnep'
>>> Extest.doppel("pengdonglin")
('pengdonglin', 'nilgnodgnep')

• 编译到x86_64上面

编写setup.py如下：

#/usr/bin/env python3

from distutils.core import setup, Extension

MOD = 'Extest'
setup(name=MOD, ext_modules=[Extension(MOD, sources=['Extest.c'])])

编译

$/usr/local/bin/python3 ./setup.py build
running build
running build_ext
building 'Extest' extension
creating build
creating build/temp.linux-x86_64-3.6
gcc -pthread -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -I/usr/local/include/python3.6m -c Extest.c -o build/temp.linux-x86_64-3.6/Extest.o
creating build/lib.linux-x86_64-3.6
gcc -pthread -shared build/temp.linux-x86_64-3.6/Extest.o -o build/lib.linux-x86_64-3.6/Extest.cpython-36m-x86_64-linux-gnu.so

可以看到，在Python3上面用setup.py默认生成的so的名字是Extest.cpython-36m-x86_64-linux-gnu.so

安装

$sudo /usr/local/bin/python3 ./setup.py install
[sudo] password for pengdonglin: 
running install
running build
running build_ext
running install_lib
copying build/lib.linux-x86_64-3.6/Extest.cpython-36m-x86_64-linux-gnu.so -> /usr/local/lib/python3.6/site-packages
running install_egg_info
Writing /usr/local/lib/python3.6/site-packages/Extest-0.0.0-py3.6.egg-info

可以看到，将Extest.cpython-36m-x86_64-linux-gnu.so拷贝到了/usr/local/lib/python3.6/site-packages下面。

测试

在PC上面输入python3命令：

$python3
Python 3.6.0 (default, Mar 23 2017, 10:40:28) 
[GCC 4.8.4] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import Extest
>>> Extest
<module 'Extest' from '/usr/local/lib/python3.6/site-packages/Extest.cpython-36m-x86_64-linux-gnu.so'>
>>> Extest.fac(4)
24
>>> Extest.reverse("pengdonglin")
'nilgnodgnep'
>>> Extest.doppel("pengdonglin")
('pengdonglin', 'nilgnodgnep')
>>> 

可以在第7行看到加载的Extest.so的路径，而且我们只需要import Extest就可以了。

完。