avoid importing yt at import time, since it imports a lot of submodules we generally don't need.  There was excess error checking also, since we really only care about yt being importable when certain functions are called
avoid importing yt at import time, since it imports a lot of submodules
we generally don't need.  There was excess error checking also, since we
really only care about yt being importable when certain functions are
called

low-sky/spectral-cube,keflavich/spectral-cube,radio-astro-tools/spectral-cube,e-koch/spectral-cube,jzuhone/spectral-cube