Fetching some items from the database, creating a grouped list of those items with a bunch of calculations on related items... sounds super-easy in python. Alas, in my use case,it made me include a "please wait while we're generating the data" modal in the frontend.
That's when I remembered a dear friend saying “Whatever it is you have to do, Postgres can do it, and fast!” Enter the ORM and its deep bag of tricks- chained annotations, subqueries, window functions, conditionals-in-query, digging into JSONB-arrays, and all this with no raw SQL (almost).