Recall without looking
What type does csv.DictReader return? Why hash an input? How should a zero denominator behave?
Check and explain
CSV fields begin as strings. Hashes identify bytes, not truth. A zero denominator is undefined and needs an explicit unavailable result; zero is a different claim.
Transfer task
Read the retail file, validate IDs/status and sum integer cents from memory. Test a malformed amount and describe the failure policy.
Record your next review
Write which concept you missed and one new example. Revisit after 2–3 days, then about a week; adjust the interval to your needs. This is a suggested study routine, not an automated reminder or saved score.
Try the activity before reading its reference. Keep your sources, commands and assumptions with your work. Companion activities are unsaved self-practice and do not award a certificate or change lesson progress.