[Python] Numpy distutils not recognizing Fortran file types

I am trying to write a python package with Anaconda3 which includes some compiled Fortran libraries. Based on the examples given online, I need to use numpy.distutils.core.Extension to have the extension build correctly. Here is my somewhat-minimal working example directory:

MANIFEST.in
setup.py
bin
└─── test_smat
mypkg
├─── __init__.py
├─── compiled
| ├─── __init__.py
| └─── gaussian.f90
└─── pystuff
├─── __init__.py
└─── buildmat.py


MANIFEST.in contains:

recursive-include mypkg *.f90


setup.py contains:

from setuptools import find_packages
from setuptools import setup
from numpy.distutils.core import Extension


ext_modules = [
Extension('mypkg.compiled.gaussian',
sources=['mypkg/compiled/gaussian.f90'])
]


setup(
name='mypkg',
version='0.1',
description='This should work',
packages=find_packages(),
scripts=['bin/test_smat'],
install_requires=['numpy>=1.7.0'],
ext_modules = ext_modules
)


gaussian.f90 contains (EDIT: simplified):

!
! Calculates the overlap between two Gaussians
!
subroutine overlap(x1, x2, a1, a2, S)
implicit none
double precision, intent(in) :: x1, x2, a1, a2
double precision, intent(out) :: S

double precision, parameter :: pi=atan(1.0_8)
double precision :: N1, N2, dist, expt

N1 = (pi / (2*a1)) ** (-0.75)
N2 = (pi / (2*a2)) ** (-0.75)
dist = abs(x2 - x1)
expt = a1*a2*dist**2 / (a1 + a2)
S = N1 * N2 * exp(-expt) * (pi / (a1 + a2)) ** 1.5

return
end subroutine overlap


buildmat.py contains:

"""
Module for building matrices of Gaussian properties
"""
import numpy as np
import mypkg.compiled.gaussian as gaussian


def olap_matrix(x, a):
"""Builds an overlap matrix from a set of positions and widths."""
ngauss = len(x)
Smat = np.empty((ngauss, ngauss))

for i in range(ngauss):
for j in range(ngauss):
Smat[i,j] = gaussian.overlap(x, x[j], a, a[j])

return Smat


test_smat contains:

#!/usr/bin/env python
"""
Script to test Python modules depending on Fortran libraries.
"""
import mypkg.pystuff.buildmat as buildmat


def main():
"""The main routine."""
x = [-1, -0.9, -0.5, -0.1, 0.0, 0.0001, 0.001, 0.01, 0.1]
a = [1.2, 0.8, 0.3, 1.5, 3.2, 0.9, 0.8, 0.1, 1.6]
mat = buildmat.olap_matrix(x, a)

print(mat)


if __name__ == '__main__':
main()


Ideally, I should be able to install with python setup.py install and run test_smat to get a printed output. However, when I try to install I get:

running install
running bdist_egg
running egg_info
writing mypkg.egg-info/PKG-INFO
writing dependency_links to mypkg.egg-info/dependency_links.txt
writing requirements to mypkg.egg-info/requires.txt
writing top-level names to mypkg.egg-info/top_level.txt
reading manifest file 'mypkg.egg-info/SOURCES.txt'
reading manifest template 'MANIFEST.in'
writing manifest file 'mypkg.egg-info/SOURCES.txt'
installing library code to build/bdist.linux-x86_64/egg
running install_lib
running build_py
creating build
creating build/lib.linux-x86_64-3.6
creating build/lib.linux-x86_64-3.6/mypkg
copying mypkg/__init__.py -> build/lib.linux-x86_64-3.6/mypkg
creating build/lib.linux-x86_64-3.6/mypkg/pystuff
copying mypkg/pystuff/buildmat.py -> build/lib.linux-x86_64-3.6/mypkg/pystuff
copying mypkg/pystuff/__init__.py -> build/lib.linux-x86_64-3.6/mypkg/pystuff
creating build/lib.linux-x86_64-3.6/mypkg/compiled
copying mypkg/compiled/__init__.py -> build/lib.linux-x86_64-3.6/mypkg/compiled
running build_ext
building 'mypkg.compiled.gaussian' extension
C compiler: gcc -pthread -B /home/rymac/.anaconda3/compiler_compat -Wl,--sysroot=/ -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC

error: unknown file type '.f90' (from 'mypkg/compiled/gaussian.f90')


Am I missing something that tells NumPy distutils that the extension is a Fortran 90 file? Other examples on this website seem to have a setup.py file that is just as simple without encountering this error. Changing the Fortran extension to .f95 or .f leads to the same type of error.

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