_scal.cpp

#include <pybind11/pybind11.h>
#include <pybind11/numpy.h>
#include <numpy/arrayobject.h>

namespace py = pybind11;

template<typename T>
py::object create_numpy_scalar(T val) {
    // usage requires initialized NumPy C-API (call _imoprt_array() before use)
    py::object dt = py::dtype::of<T>();
    PyObject * scal = PyArray_Scalar(&val, (PyArray_Descr*)dt.ptr(), py::int_(sizeof(T)).ptr());
    return py::reinterpret_steal<py::object>(scal);
}

PYBIND11_MODULE(_scal, m) {

    if (_import_array() < 0) {
        PyErr_SetString(PyExc_ImportError, "numpy.core.multiarray failed to import");
    }

    m.doc() = "pyarray_scalar demo, run like: $ python3 setup.py build_ext -i && python3 test_scal.py";
    m.def("get_scalar", []() { return create_numpy_scalar(42.0); });
}

setup.py

from setuptools import setup, Extension
import pybind11
ext_mod = Extension(
    '_scal', ['_scal.cpp'],
    language='c++', extra_compile_args=['-std=c++14', '-fmax-errors=3'],
    include_dirs=[pybind11.get_include(), pybind11.get_include(user=True)])
setup(name='_scal', ext_modules=[ext_mod])

test_scal.py

from _scal import get_scalar
print(get_scalar())