1) coding via repl - e.g. one emacs buffer has stored procedure code, send functions over via keyboard shortcut to SQL repl buffer connected to DB to evaluate it 'live' (jupyter notebooks are basically a copy of this mode of operation in a more consumer-friendly package)

2) w/r/t python in db, as OP mentions pgsql, pgsql has support for in-db extensibility using a variety of languages, of which python is one: https://www.postgresql.org/docs/current/plpython.html probably referring to this