The ebuild of vigra currently has only python 2.7 support but according to the homepage (https://ukoethe.github.io/vigra/) it already supports at least python 3.4 and 3.5.

Tests with a modified ebuild show that it at least emerges with python 3.7, although the required threads USE flag has to be disabled for that, as it is not available in python 3.7.

According to this issue on github (https://github.com/ukoethe/vigra/issues/450) the support of python 3.7 should be possible.