When importing tensorflow, I get the following error: No module named 'numpy.core._multiarray_umath'

I also had the same issue. It got resloved once i upgraded the numpy from 1.15.4 to 1.16.1.

If you're using pip: pip install numpy --upgrade

Numpy that came with Anaconda3 is of version 1.15.4. so i upgraded and it worked.

Side note: if you're also using scikit-image in your script, be aware that numpy 1.16.3 has a conflict with old versions of scikit-image (e.g. you may get ImportError: cannot import name '_validate_lengths'). In that case, pip install --upgrade scikit-image from terminal solved the issue for me.

Hope it helps!!