Python script import from PATH in C++

Question

I'm trying to run a Python script in a C++ program using Python.h. Because this C++ program can be installed (make install) in /usr/bin, it needs to be able to find the Python script both in its own directory (in case it was not installed) or in one of the PATH environment variable's directories.

I have tried doing :

PyObject *pName = PyString_FromString(scriptName); // scriptName is "file.py" as a char*
PyRun_SimpleString("import sys");
PyRun_SimpleString("sys.path.append(\".\")");
PyObject *pModule = PyImport_Import(name); // not working because absolute path only
                                           //since Python 2.7 ?

and

PyRun_SimpleString("import sys");
PyRun_SimpleString("sys.path.append(\".\")");
PyObject *pModule = PyImport_ImportModuleEx(scriptName, NULL, NULL, NULL);

But both leave me with pModule == NULL after this call but work if I run the C++ module from its own directory.

Thanks a lot for your help

Few questions: 1) Will the application be run from the directory containing the python script? 2) Have you tried calling PySys_SetArgvEx before Py_Initialize, and setting the application path? — Dustin Anderson
– Dustin Anderson, Commented Jul 2, 2013 at 16:23
1) Absolutely, make puts the C++ executable in the same directory where the Python script is located. make install copies both the C++ executable and the Python script in usr/bin (or wherever the user wants to install those). 2) I have not, mostly because this part of the C++ program is pretty far away from the main and thus of the original argc and argv variables. Do I need to do that to set the application path ? — wrousseau
– wrousseau, Commented Jul 2, 2013 at 16:30

pafinde · Accepted Answer · 2013-07-05 21:30:38Z

2

"." works as a path to your python scripts only if your C++ python script's root directory is the current working directory of your process.

If your program was started from somewhere else (either via PATH or by /path/to/a/program) then the only reliable way to find your scripts is to use use your argv[0] param from main.

Once you find the correct path, there are two ways to use it:

pass it to sys.path.append
switch the working directory there using chdir (from unistd.h), and then you can pass "." to sys.path.append. The chdir will affect the whole process, but pros is that you can do it directly in main.

answered Jul 5, 2013 at 21:30

pafinde

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1 Comment

wrousseau Over a year ago

That's what I fear, from what I read, studying argv[0] is not a fully reliable thing to do... Thanks for the clear answer however !

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