15.17 傳遞文件名給C擴(kuò)展

問題

You need to pass filenames to C library functions, but need to make sure the filenamehas been encoded according to the system’s expected filename encoding.

解決方案

To write an extension function that receives a filename, use code such as this:

static PyObject *py_get_filename(PyObject *self, PyObject *args) {
PyObject *bytes;char *filename;Py_ssize_t len;if (!PyArg_ParseTuple(args,”O(jiān)&”, PyUnicode_FSConverter, &bytes)) {

return NULL;

}PyBytes_AsStringAndSize(bytes, &filename, &len);/ Use filename [](#)/...

/ Cleanup and return [](#)/Py_DECREF(bytes)Py_RETURN_NONE;

}

If you already have a PyObject * that you want to convert as a filename, use code suchas the following:

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 filenamelen; / Already set */

PyObject *obj = PyUnicode_DecodeFSDefaultAndSize(filename, filename_len);

討論

Dealing with filenames in a portable way is a tricky problem that is best left to Python.If you use this recipe in your extension code, filenames will be handled in a manner thatis consistent with filename handling in the rest of Python. This includes encoding/decoding of bytes, dealing with bad characters, surrogate escapes, and other complica‐tions.