Posts tagged #domain-driven-design

Don't let the LLM do the math: deterministic discount proration for receipt OCR

August 7, 202610 min

#python
#llm

A vision model reads the receipt fine, then quietly loses a cent splitting the discount. Here's why I moved the arithmetic out of the model into a small Python function whose shares always sum to the amount paid.

Credit-card billing cycles: domain logic and a migration that freezes history

July 25, 20268 min

#python
#django

The day you swipe a card is not the month you're accounting for. Here's how I modelled credit-card billing cycles as a pure function, applied it in one save hook, and used an irreversible migration to stop a future rule change from rewriting the past.