Django Text Search With Partial Sentence Match Update To Django3

I am trying to apply partial search in Django postgres, exactly the same as described here django-text-search-with-partial-sentence-match I found there a pretty nice solution from

Solution 1:

So we're clear, your problem here is not with the Python version, but with the Django version.

What you're looking for should be self.source_expressions[0].

However if I were rewriting this today, I'd start by looking at the raw search type (example) and pass my own query using the proximity operator <-> (example).