Before it was easy just to write

import rethinkdb as r

conn = r.connect(...)
r.table(...).run(conn)

But documentation (simply README) of rethinkdb python driver >=2.4.0 insist that now the proper way to do it is this:

from rethinkdb import RethinkDB

r = RethinkDB()
conn = r.connect(...)
r.table(...).run(conn)

It's OK to do it in single function. But it is NOT OK to do it in multiple functions and pass around the rethinkdb_instance parameter in each function that makes requests to your rethinkdb.