3D Polyhedron load from file fails with Can't find wavefront object file

Error message

Traceback (most recent call last):
  File "polyhedron_3d.py", line 389, in <module>
    Poly3D().run()
  File "/Applications/Inkscape.app/Contents/Resources/share/inkscape/extensions/inkex/base.py", line 140, in run
    self.save_raw(self.effect())
  File "/Applications/Inkscape.app/Contents/Resources/share/inkscape/extensions/inkex/extensions.py", line 151, in effect
    fragment = self.generate()
  File "polyhedron_3d.py", line 303, in generate
    obj = WavefrontObj(self.get_filename())
  File "polyhedron_3d.py", line 190, in __init__
    self._parse_file(filename)
  File "polyhedron_3d.py", line 194, in _parse_file
    raise IOError("Can't find wavefront object file {}".format(filename))
OSError: Can't find wavefront object file great_rhombicuboct.obj