Determining path of the translated cython pyx source file - cython

Question

I have a cython source file in which I would like to import the local python module.
This cython source file is translated using cython (python3 syntax) into a c++ source, which in turn is compiled into a library, and then used from the main C++ program.
When the main program is being executed the import of the local python module fails because the location of thereof module is not known to the executed code. I tried using python3's local import features in my pyx file but to no avail.
The only working solution I came up with (and the most obvious one) is to update python's module search path using sys.path.append. The problem is that I have to hardcode this path, which is ugly.
I tried to find any hints if it is possible to retrieve within cython code location of the source file (I could derive an absolute path from it) but without success. Usual pythonic ways to do that fail - for instance, one of the reasons is that __file__ evaluates to built-in, and retrieval of the absolute path at runtime gives the path where the executable is being run.
Sidenote: one of the searches I did was by querying GitHub search engine for occurrences of sys.path.append in cython files. Interestingly, all results either have paths hardcoded or they are not related to the location of the cython source file within the file system.
So my question is if it is possible within cython code to reliably retrieve the location of its source file?
Disclaimer: I could imagine instrumenting the build system to pass preprocessor variable set to the path in question while building the C++ file derived from the cython one, and then access this within the code, but this looks like an overkill.
Example:
bulba.py
def fn():
print('blah')
bulbulator.pyx
# tag: cpp
# tag: py3only
import sys
sys.path.append('/absolute_path_to_folder_with_bulba_py') # <-- this is the key part. I'd like to replace the hardcoded path with something better
from bulba import fn
fn()
bulbulator.pyx is translated into cpp with:
cython -3 --cplus bulbulator.pyx
lib_wrapper.cpp (this library, and executable which links against it, have a location different than that of py/pyx source code and its translated c++ part)
// import headers generated by cython
#include "bulbulator_api.h"
#include "bulbulator.h"
// global initialization of the cythonized part
__attribute__((constructor))
static void
__library_init()
{
if (int err = PyImport_AppendInittab("bulbulator", PyInit_bulbulator); err != 0)
{
std::fprintf(stderr, "PyImport_AppendInittab(bulbulator) failed with status code=%d\n", err);
std::exit(1);
}
Py_Initialize();
if (import_bulbulator() == -1) // <-- here it fails if I comment out sys.path.append, because bulbulator needs to know the location of bulba.py
{
PyErr_Print();
}
}

Answer 1

I would rather put the bulba.py next to the exe, but it is also possible to back in an absolute path into the Cython-extension, using for example a compile time environment variable (see cython --help for more details), let's call it ADDITIONAL_SYS_PATH:
import sys
sys.path.append(ADDITIONAL_SYS_PATH)
from bulba import fn
fn()
And now running Cython via:
cython -3 --cplus -E ADDITIONAL_SYS_PATH="the path to dir"
will set the right value to ADDITIONAL_SYS_PATH.
Cython saves the name of the pyx-file in the resulting cpp (for example for run-time error reporting), but this name doesn't include the full path, so we need to provide the path manually.