Python CLI Tool to Turn CSV Exports Into Monthly Invoices

Every month we export a CSV of billable hours from our time tracker and someone on the team spends most of a day turning it into individual client invoices by hand in Word. It is slow and we make mistakes on it. I want a small command line tool we run on our own machines. It reads the CSV, groups the hours by client, applies each client’s hourly rate, and produces one PDF invoice per client into a folder. Nothing hosted, nothing fancy, no login screen. It should tell us clearly if a row in the CSV is missing a client or a rate rather than producing a wrong invoice quietly. We have the CSV format and a Word invoice we currently use as the layout to match. Please share something similar you have built.