Choose Python’s core collection types based on ordering, uniqueness, mutability, and lookup needs.
The core idea
Lists preserve order and allow duplicates. Tuples are ordered and commonly represent fixed records. Sets store unique values and support fast membership checks. Dictionaries map keys to values and are useful for lookups by identifier.
A practical way to approach it
Ask what operation dominates the task. If you need to preserve every item in sequence, use a list. If you repeatedly ask whether an item has appeared, consider a set. If you look up details by a stable key, use a dictionary. Use a tuple for a small fixed group of related values when that communicates intent.
Try it in a small project
For a course tracker, store lesson order in a list, completed lesson IDs in a set, and lesson details in a dictionary keyed by ID. Keep the source of truth clear so these structures do not drift apart.
Common mistakes to avoid
Do not choose a collection only because it is familiar. Consider ordering, duplicates, mutability, and memory when the data becomes large.
Key takeaway
Keep the first version small, make your assumptions explicit, and verify the result with a repeatable test. For production use, check the current official documentation for the tools and versions you choose.