传递文件名给C扩展

写一个接受一个文件名为参数的扩展函数，如下这样：

static PyObject *py_get_filename(PyObject *self, PyObject *args) {
  PyObject *bytes;
  char *filename;
  Py_ssize_t len;
  if (!PyArg_ParseTuple(args,"O&", PyUnicode_FSConverter, &bytes)) {
    return NULL;
  }
  PyBytes_AsStringAndSize(bytes, &filename, &len);
  /* Use filename */
  ...

  /* Cleanup and return */
  Py_DECREF(bytes)
  Py_RETURN_NONE;
}
如果你已经有了一个 PyObject * ，希望将其转换成一个文件名，可以像下面这样做：

PyObject *obj;    /* Object with the filename */
PyObject *bytes;
char *filename;
Py_ssize_t len;

bytes = PyUnicode_EncodeFSDefault(obj);
PyBytes_AsStringAndSize(bytes, &filename, &len);
/* Use filename */
...

/* Cleanup */
Py_DECREF(bytes);

If you need to return a filename back to Python, use the following code:

/* Turn a filename into a Python object */

char *filename;       /* Already set */
int   filename_len;   /* Already set */

PyObject *obj = PyUnicode_DecodeFSDefaultAndSize(filename, filename_len);