swe-hiring/part1-pricing/README.md

Part 1 — Pricing: discount stacking

pricing/discounts.py contains apply_discounts(), used by our billing service to price orders that carry one or more percentage discounts. The current implementation does not follow the billing rules below, and part of the test suite fails because of it.

Your task

Update apply_discounts() so it implements the billing rules. Run the tests with:

pip install -e ".[dev]"
python -m pytest

Billing rules (specification)

1. base_price is a non-negative number. A negative base_price raises ValueError.

2. discounts is a sequence of percentages. Each discount must be within 0–100 inclusive; any discount outside that range raises ValueError.

3. Stacking is sequential (compounding). Each discount applies to the price left over by the previous one — discounts are never summed.

   Example: 100.00 with discounts [10, 20]:

   • after 10%: 90.00
   • after 20% of the remainder: 72.00 ← final price

4. The result is rounded to 2 decimal places.

That is the whole specification. When you are done, note anything worth mentioning in the repository-level NOTES.md.