Initialize a sub-module within a package with SWIG and Python 3

Question

I have a C++ application that I swigged to Python 2.7. I'm currently trying to port my code from Python 2.7 to Python 3.4 using the Python/C API and SWIG.

I have a package containing multiple modules. The problem is I cannot find a way to initialize my module ModuleABC as a sub-module of package PackageXYZ. It works well with Python 2.7 but not with Python 3.4 (and I suppose it wouldn't work either with any Python 3.x version).

Here is my code.

ModuleABC.h

extern "C"
{
#if PY_MAJOR_VERSION >= 3
    PyObject* PyInit__ModuleABC(void);
#else
    void init_ModuleABC(void);
#endif
}

void InitModule()
{
 // Defined in the SWIG generated cpp file

#if PY_MAJOR_VERSION >= 3
    PyImport_AppendInittab("PackageXYZ.ModuleABC", PyInit__ModuleABC);
#else
    init_ModuleABC();
#endif
}

PythonManager.cpp

void initPythonInterpreter()
{
    Py_SetPythonHome("C:\Python34");

    Py_SetProgramName("MyApp.exe");

    #if PY_MAJOR_VERSION < 3
       // For Python 2.7 
       Py_Initialize();
    #endif

    // Init module
    ModuleABC.InitModule();

    #if PY_MAJOR_VERSION >= 3
        // For Python 3.4
        Py_Initialize();
    #endif

    int nResult = 0;

    // Import package
    nResult += PyRun_SimpleString("import PackageXYZ");

    // Import module
    // ERROR: Works with Python 2.7, but not with Python 3.4
    nResult += PyRun_SimpleString("import PackageXYZ.ModuleABC");
}

If I change the line:

PyRun_SimpleString("import PackageXYZ.ModuleABC");

to:

PyRun_SimpleString("import ModuleABC");

then it runs with no error, but my module is not imported within the package.

Any ideas?

Why are you using PyRun_SimpleString instead of PyImport_ImportModule? — Flexo - Save the data dump
– Flexo - Save the data dump ♦, Commented Jul 23, 2014 at 20:37
Just because I was doing some tests. Both commands give same results. — MasterMind
– MasterMind, Commented Jul 23, 2014 at 20:41

MasterMind · Accepted Answer · 2014-09-03 13:22:34Z

1

I've finally found the problem. When using PyImport_AppendInittab with SWIG and Python 3 in embedded mode, you need to put the "underscore" before the name of the module, without the package name.

PyImport_AppendInittab("_myModule", PyInit__myModule);

Just make sure your files structure is of the form:

myPackage\
   __init__.py
   myModule.py

Then everything works as expected.

answered Sep 3, 2014 at 13:22

MasterMind

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