JSON keys are strings, but the ids are numbers

total_for_ids(counts, ids) totals the counts for the given ids. counts comes from a JSON payload, e.g. {"1": 10, "2": 20}, and ids are integers.

total_for_ids({"1": 10, "2": 20}, [1, 2]) raises KeyError: 1 — even though the key is plainly there in the dict.