Step by step to write python extension in C language

This article introduces how to extend python with C language. The example given is to add a function to Python to set a string to the Windows Clipboard. The environment I used when writing the following code is: windows xp, gcc.exe 4.7.2, Python 3.2.3.

The first step is to write a C language DLL

Create a clip.c file with the following content:

// 设置 UNICODE 库，这样的话才可以正确复制宽字符集
#define UNICODE
  
#include <windows.h>
#include <python.h>
  
// 设置文本到剪切板(Clipboard)
static PyObject *setclip(PyObject *self, PyObject *args)
{
  LPTSTR  lptstrCopy;
  HGLOBAL hglbCopy;
  Py_UNICODE *content;
  int len = 0;
  
  // 将 python 的 UNICODE 字符串及长度传入
  if (!PyArg_ParseTuple(args, "u#", &content, &len))
    return NULL;
  
  Py_INCREF(Py_None);
  
  if (!OpenClipboard(NULL))
    return Py_None;
  
  EmptyClipboard();
  
  hglbCopy = GlobalAlloc(GMEM_MOVEABLE, (len+1) * sizeof(Py_UNICODE));
  if (hglbCopy == NULL) {
    CloseClipboard();
    return Py_None;
  }
  
  lptstrCopy = GlobalLock(hglbCopy);
  memcpy(lptstrCopy, content, len * sizeof(Py_UNICODE));
  lptstrCopy[len] = (Py_UNICODE) 0;
  
  GlobalUnlock(hglbCopy);
  
  SetClipboardData(CF_UNICODETEXT, hglbCopy);
  
  CloseClipboard();
  
  return Py_None;
}
  
// 定义导出给 python 的方法
static PyMethodDef ClipMethods[] = {
  {"setclip", setclip, METH_VARARGS,
   "Set string to clip."},
  {NULL, NULL, 0, NULL}
};
  
// 定义 python 的 model
static struct PyModuleDef clipmodule = {
  PyModuleDef_HEAD_INIT,
  "clip",
  NULL,
  -1,
  ClipMethods
};
  
// 初始化 python model
PyMODINIT_FUNC PyInit_clip(void)
{
  return PyModule_Create(&clipmodule);
}

The second step is to write the python setup.py

Create a setup.py file with the following content:

from distutils.core import setup, Extension
  
module1 = Extension('clip',
                    sources = ['clip.c'])
  
setup (name = 'clip',
       version = '1.0',
       description = 'This is a clip package',
       ext_modules = [module1])

Chapter Three steps to compile with python

Run the following command:

python setup.py build --compiler=mingw32 install

In my environment, the following error will be prompted:

gcc: error: unrecognized command line option '-mno- cygwin'

error: command 'gcc' failed with exit status 1

Open the %PYTHON installation directory%/Lib/distutils/cygwinccompiler.py file, delete -mno-cygwin in it, and then run it again.

After normal operation, a clip.pyd file will be generated and copied to the %PYTHON installation directory%/Lib/site-packages directory

The fourth step is to test the extension

Write A test.py, the content is as follows:

# -*- encoding: gbk -*-
import clip
clip.setclip("Hello python")

Run

python test.py

and then paste it anywhere to verify whether it is correct.