JSON and CSV

json.loads turns a JSON string into Python objects and json.dumps goes the other way. Nested structures become nested dicts and lists.

csv.DictReader reads rows as dictionaries keyed by the header. Here we read from a string so the example runs in the browser; in a script you would pass an open file instead.

Always convert CSV values explicitly — everything arrives as a string, and silently summing strings is a classic bug.