Sample C extension module in Python. Fetches a URL using libcurl.

curly.c

#include <Python.h>
#include <curl/curl.h>

typedef struct Bucket {
  char *contents;
  size_t size;
} Bucket;

static PyObject *CurlyError;

static size_t fill_bucket_callback(void *contents, size_t size, size_t nmemb,
                                   void *userdata)
{

  size_t total_size = size * nmemb;
  Bucket *bucket = (Bucket *)userdata;

  bucket->contents = realloc(bucket->contents, bucket->size + total_size + 1);

  if (bucket->contents == NULL) {
    return 0;
  }

  memcpy(&(bucket->contents[bucket->size]), contents, total_size);
  bucket->size += total_size;
  bucket->contents[bucket->size] = 0;

  return total_size;
}

static char *fetch(const char *url)
{
  CURL *curl;
  CURLcode res;
  Bucket bucket;

  bucket.contents = malloc(0);
  bucket.size = 0;

  if (bucket.contents == NULL) {
    return NULL;
  }

  curl = curl_easy_init();

  if (curl) {
    curl_easy_setopt(curl, CURLOPT_URL, url);
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, fill_bucket_callback);
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, (void *)&bucket);
    curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);

    res = curl_easy_perform(curl);

    if (res != CURLE_OK) {
      PyErr_SetString(CurlyError, curl_easy_strerror(res));
      return NULL;
    }

    curl_easy_cleanup(curl);
  }

  return bucket.contents;
}

/* Python interface */

static PyObject *curly_fetch(PyObject *self, PyObject *args)
{
  const char *url, *body;

  if (!PyArg_ParseTuple(args, "s", &url)) {
    return NULL;
  }

  body = fetch(url);

  if (body == NULL) {
    return NULL;
  }

  return PyUnicode_FromString(body);
}

static PyMethodDef CurlyMethods[] = {
  {"fetch", curly_fetch, METH_VARARGS, "Fetch the body of a webpage."},
  {NULL, NULL, 0, NULL}
};


PyMODINIT_FUNC initcurly(void)
{
  PyObject *module = Py_InitModule("curly", CurlyMethods);

  if (module == NULL) {
    return;
  }

  CurlyError = PyErr_NewException("curly.CurlyError", NULL, NULL);
  Py_INCREF(CurlyError);
  PyModule_AddObject(module, "CurlyError", CurlyError);
}

setup.py

from distutils.core import setup, Extension

curly = Extension('curly',
                  libraries=['curl'],
                  sources=['curly.c'])

setup(name='Curly',
      version='0.1.1',
      author='Ryan Kaskel',
      author_email='dev@ryankaskel.com',
      ext_modules=[curly])