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 < )
         return ;
     return n * fac(n - );
 }

 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) - ));
     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,
     -,
     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-.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./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./site-packages/
 [root@aarch64 root]# python3
 Python 3.6. (default, Mar  , ::)
 [GCC 4.9.  (prerelease)] on linux
 Type "help", "copyright", "credits" or "license" for more information.
 >>> import Extest
 >>> Extest.fac()

 >>> 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./site-packages
 running install_egg_info
 Writing /usr/local/lib/python3./site-packages/Extest-0.0.-py3..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. (default, Mar  , ::)
 [GCC 4.8.] 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()

 >>> 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。