A data structure holds many values together. Python's four everyday ones, and when to reach for each:

• list [ ] — an ordered collection you can change. Use for: a sequence of things, like prices.
• tuple ( ) — like a list but can't change. Use for: fixed groups, like a coordinate.
• dict {key: value} — labelled values. Use for: describing one thing, like a student.
• set { } — unique values, no duplicates. Use for: "which different items appeared?"

The next lessons take tuples and sets one at a time.