ImportError: dynamic module does not define init function

I am trying to reproduce the following tutorial https://csl.name/post/c-functions-python/.

My Python extension in C++ looks like:

#include <Python.h>

static PyObject* py_myFunction(PyObject* self, PyObject* args)
{
  char *s = "Hello from C!";
  return Py_BuildValue("s", s);
}

static PyObject* py_myOtherFunction(PyObject* self, PyObject* args)
{
  double x, y;
  PyArg_ParseTuple(args, "dd", &x, &y);
  return Py_BuildValue("d", x*y);
}

static PyMethodDef extPy_methods[] = {
  {"myFunction", py_myFunction, METH_VARARGS},
  {"myOtherFunction", py_myOtherFunction, METH_VARARGS},
  {NULL, NULL}
};

void initextPy(void)
{
  (void) Py_InitModule("extPy", extPy_methods);
}

I am using the following setup.py:

from distutils.core import setup, Extension
setup(name='extPy', version='1.0',  \
ext_modules=[Extension('extPy', ['extPy.cpp'])])

After invoking it with python setup.py install the .so file seems to be in the right place.

But when I try to use this extension with import extPy I get the Error:

ImportError: dynamic module does not define init function

What am I missing here? Thanks for Help.

Copyright Notice：Content Author:「P Alcove」，Reproduced under the CC 4.0 BY-SA copyright license with a link to the original source and this disclaimer.
Link to original article：https://stackoverflow.com/questions/28040833/importerror-dynamic-module-does-not-define-init-function