Gentoo's Bugzilla –
Attachment 633298 Details for
Bug 717812media-libs/opencv-4.1.2-r3 - In file included from .../work/opencv-4.1.2/modules/python/src2/cv2.cpp:30: /usr/lib64/python3.6/site-packages/numpy/core/include/numpy/numpyconfig.h:4:10: fatal error: _numpyconfig.h: No such file or directory