[3.1] Convolve problems in some affiliated packages

I just uploaded astropy 3.1 to Debian (which succeeds all its own tests on build time), and found that gammapy now shows some CI test errors:

__________ ERROR collecting astro/darkmatter/tests/test_profiles.py ___________
ImportError while importing test module '/usr/lib/python3/dist-packages/gammapy/astro/darkmatter/tests/test_profiles.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/usr/lib/python3/dist-packages/astropy/convolution/convolve.py:27: in <module>
    _convolve = load_library("_convolve", LIBRARY_PATH)
/usr/lib/python3/dist-packages/numpy/ctypeslib.py:131: in load_library
    from numpy.distutils.misc_util import get_shared_lib_extension
/usr/lib/python3/dist-packages/numpy/distutils/__init__.py:6: in <module>
    from . import ccompiler
/usr/lib/python3/dist-packages/numpy/distutils/ccompiler.py:11: in <module>
    from distutils import ccompiler
E   ImportError: cannot import name 'ccompiler' from 'distutils' (/usr/lib/python3.7/distutils/__init__.py)

During handling of the above exception, another exception occurred:
/usr/lib/python3/dist-packages/gammapy/astro/darkmatter/__init__.py:4: in <module>
    from .spectra import *
/usr/lib/python3/dist-packages/gammapy/astro/darkmatter/spectra.py:9: in <module>
    from ...spectrum.models import TableModel
/usr/lib/python3/dist-packages/gammapy/spectrum/__init__.py:4: in <module>
    from .observation import *
/usr/lib/python3/dist-packages/gammapy/spectrum/observation.py:12: in <module>
    from ..irf import EffectiveAreaTable, EnergyDispersion, IRFStacker
/usr/lib/python3/dist-packages/gammapy/irf/__init__.py:10: in <module>
    from .psf_gauss import *
/usr/lib/python3/dist-packages/gammapy/irf/psf_gauss.py:9: in <module>
    from astropy.convolution import Gaussian2DKernel
/usr/lib/python3/dist-packages/astropy/convolution/__init__.py:10: in <module>
    from .convolve import convolve, convolve_fft, interpolate_replace_nans, convolve_models  # noqa
/usr/lib/python3/dist-packages/astropy/convolution/convolve.py:29: in <module>
    raise ImportError("Convolution C extension is missing. Try re-building astropy.")
E   ImportError: Convolution C extension is missing. Try re-building astropy.

It seems that #7293 caused this. I already filed gammapy/gammapy#1974, but when looking into the stacktrace again, it looks more a bug in astropy, right? Photutils has the same problem, as seen here; also radio-beam, spectral-cube and others. It may well be that my specific build was done errornously; however I am then wondering why the build time tests succeeded. Build log (including tests) is here. I couldn’t find anything that did not build there. This happens with numpy 1.16rc1 (which is now in Debian unstable); I applied #8264 to my package to make it compatible. Maybe I missed something here?

[olebole]

@saimn the missing distutils package was the cause of the problem, thank you very much for the hint! I don’t know whether this should be added to setup.py, so I leave it open for that case. Pls close otherwise.

[saimn]

distutils is part of the stdlib so there is no point in adding it to setup.py, it is not an external package, and the issue is only because of the way debian package it. Also, thinking again about this, distutils should be a (debian) dependency for numpy instead of astropy, as astropy only use it via numpy.distutils.