python-numpy-1.13.1-1 seems to need a rebuild. The file /usr/lib/python3.6/site-packages/numpy/core/multiarray.cpython-36m-x86_64-linux-gnu.so links against libgfortan.so.3, but gcc-libs comes with libgfortran.so.4 (since gcc7 I guess). I've actually got gcc-libs-multilib-7.1.1-3 installed, but the same is true for gcc-libs-7.1.1-3.

python2-numpy-1.13.1-1 has the same problem, it also links against libgfortran.so.3 .

$ ldd /usr/lib/python3.6/site-packages/numpy/core/multiarray.cpython-36m-x86_64-linux-gnu.so | grep libgfortran
libgfortran.so.3 => not found

The problem can be triggered by running a python shell and executing: import numpy

That results in the following error (snipped a bit, the important parts are there I think):

>>> import numpy
Traceback (most recent call last):
File "/usr/lib/python3.6/site-packages/numpy/core/__init__.py", line 16, in <module>
from . import multiarray
ImportError: libgfortran.so.3: cannot open shared object file: No such file or directory