Error when creating python module

Question

I have a C code which calls a Fortran subroutine called SetFlags. I would like to turn this C code into a python module. It creates a .so file, but I cannot import this module into python. I am not sure if my error is in the creation of the module using distutils or in linking to the fortran library. Here is my setflagsmodule.c file

#include <Python/Python.h>
#include "/Users/person/program/x86_64-Darwin/include/Cheader.h"
#include <stdlib.h>
#include <stdio.h>

static char module_docstring[] = 
    "This module provides an interface for Setting Flags in C";

static char setflags_docstring[] = 
    "Set the Flags for program";



static PyObject * setflags(PyObject *self, PyObject *args)
{
    int *error;
    const int mssmpart;
    const int fieldren;
    const int tanbren;
    const int higgsmix;
    const int p2approx;
    const int looplevel;
    const int runningMT;
    const int botResum;
    const int tlcplxApprox;


    if (!PyArg_ParseTuple(args, "iiiiiiiiii", &error,&mssmpart,&fieldren,&tanbren,&higgsmix,&p2approx,&looplevel,&runningMT,&botResum,&tlcplxApprox))
        return NULL;

    FSetFlags(error,mssmpart,fieldren,tanbren,higgsmix,p2approx,looplevel,runningMT,botResum,tlcplxApprox); //Call fortran subroutine
    return Py_None;
}

static PyMethodDef setflags_method[] = {
    {"FSetFlags", setflags, METH_VARARGS, setflags_docstring},
    {NULL,NULL,0,NULL}
};

PyMODINIT_FUNC init_setflags(void)
{
    PyObject *m;
    m = Py_InitModule3("setflags", setflags_method, module_docstring);
        if (m == NULL)
            return;
}

Here is my setup file called setflags.py:

    from distutils.core import setup, Extension

setup(
    ext_modules=[Extension("setflags",["setflagsmodule.c"], include_dirs=['/Users/person/program/x86_64-Darwin'],
    library_dirs=['/Users/person/program/x86_64-Darwin/lib/'], libraries=['FH'])],
    )

I build the module using:

python setflags.py build_ext --inplace

When I try to import the module into python this is the result:

>>> import setflags
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: dynamic module does not define init function (initsetflags)

Does anyone have a recommendation on how to solve this ImportError?

Any help would be greatly appreciated and thank you in advance for your time.

Answer 1

The problem is very simple, but easy to miss.

Notice the error you get:

ImportError: dynamic module does not define init function (initsetflags)

Now look at your code:

PyMODINIT_FUNC init_setflags(void)

You've defined init_setflags instead of initsetflags. Just remove the extra underscore, and it should work.

---

From the documentation on The Module's Method Table and Initialization Function:

The initialization function must be named initname(), where name is the name of the module…

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The reason you often see init functions named init_foo in examples is that they're usually initializing a module _foo.so, which will then be wrapped by a pure-Python module foo.py.