Python C api PyImport_importmodule fail when the file has an import statement

Question

I tried to use the Python C api to call a function from python in C++, the test was successful.

But if I intend to import a module already importing other module, the Pymodule_findmodule will return Null even though it's there and created a compiled file. Here is my code

Py_Initialize();
PySys_SetPath("C:/Users/Mik/Documents/GitHub/youtube-dl");      
PyObject * pythonFile = PyImport_ImportModule("test2");

Here is the python filed named test2.py at that directory with a file named test_dl.py and a class called TESTDL inside it

from test_dl import TESTDL 
def someFunction(someInput):
    return 12345

As soon as I added the import line my program doesnot recognize it as module anymore

Edit: turns out the test_dl has the first line as:

 from __future__ import unicode_literals

That's the reason I got this ImportError: No module named future

Thanks!

Sounds like you might have gotten an exception when trying to import test_dl or retrieve the TESTDL object from it. — user2357112
– user2357112, Commented Feb 1, 2016 at 18:00
What does PyErr_Print() print after your call to PyImport_ImportModule("test2")? — tynn
– tynn, Commented Feb 1, 2016 at 18:22

kfx · Accepted Answer · 2016-02-01 18:59:11Z

8

A function call to PySys_SetPath() completely overwrites the Python module path. The result is that your Python script test_dl cannot find Python system modules (in this case __future__) and throws an exception.

What you need to do is to append the directory of your module to the system path instead. To do that, first query the existing value of the system path, and then add your path to it:

PyObject *sys_path = PySys_GetObject("path");
PyList_Append(sys_path, PyString_FromString("C:/Users/Mik/Documents/GitHub/youtube-dl"));

answered Feb 1, 2016 at 18:59

kfx

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3 Comments

Hongjun Han Over a year ago

Thanks so much :) Didn't realize I need the python lib as well

Joniale Over a year ago

That only works with Python >=2.7. Here a more compatible version: append_path = PYTHON_PATH ":."; //append_path = '"'PYTHON_PATH:."; setenv("PYTHONPATH", append_path, 1); //Set PYTHONPATH TO working directory

Julien Over a year ago

PyString_FromString is not compliant with python >3.5, use PyUnicode_FromString instead

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