Python | Passing Filenames to Extension in C
Last Updated :
07 Jun, 2019
Filename has to be encoded according to the system’s expected filename encoding before passing filenames to C library functions.
Code #1 : To write an extension function that receives a filename
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);
Py_DECREF(bytes)
Py_RETURN_NONE;
}
|
If there is already a existing PyObject *
that needs to be converted as a filename, then use the code given below :
Code#2 :
PyObject* obj;
PyObject* bytes;
char * filename;
Py_ssize_t len;
bytes = PyUnicode_EncodeFSDefault(obj);
PyBytes_AsStringAndSize(bytes, &filename, &len);
...
Py_DECREF(bytes);
|
If a filename is to be returned back to Python, use the following code given below –
Code #3 :
char * filename;
int filename_len;
PyObject* obj = PyUnicode_DecodeFSDefaultAndSize(
filename, filename_len);
|
Dealing with filenames in a portable way is a tricky problem that is best left to Python. Filenames will be handled in a manner that, if one uses the above in extension C code.
Passing Open Files to C Extensions –
Code #4 : To convert a file to an integer file descriptor, use PyFile_FromFd()
PyObject* fobj;
int fd = PyObject_AsFileDescriptor(fobj);
if (fd < 0) {
return NULL;
}
|
The resulting file descriptor is obtained by calling the fileno()
method on fobj. Thus, any object that exposes a descriptor in this manner should work (e.g., file, socket, etc.). A descriptor can be passed to various low-level C functions that expect to work with files. PyFile_FromFd()
is used to convert an integer file descriptor back into a Python object.
Code #5 :
int fd;
PyObject* fobj = PyFile_FromFd(fd, "filename" ,
"r" , -1, NULL, NULL, NULL, 1);
|
The arguments to PyFile_FromFd()
mirror those of the built-in open() function. NULL values simply indicate that the default settings for the encoding, errors, and newline arguments are being used.
Like Article
Suggest improvement
Share your thoughts in the comments
Please Login to comment...