Python | Passing Filenames to Extension in C
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;
}
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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);
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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;
}
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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);
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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.
Last Updated :
07 Jun, 2019
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