15.17 传递文件名给C扩展

问题¶

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

解决方案¶

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&”, 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 such as 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 filename_len; / Already set */

PyObject *obj = PyUnicode_DecodeFSDefaultAndSize(filename, filename_len);

讨论¶

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 that is 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.