Currently, it seems that the search is performed through (via the Spice class, which output results only from Python 2 docs.
The engine is not really open source, but maybe it would be possible to ask the maintener for a little upgrade. Because it doesn't look good to write a specific piece of code only for Python 3 docs.

Another possibility would be to move to as suggested by Volvox (it deals with css, html, python, js, php, xslt and jquery right now), but it is not as complete as right now.
posted by [UserVoice Arroway] • 5 years and 1 month ago Link