list vs tuple vs set vs dict — pick the right one

list

Ordered, mutable, allows duplicates. The default for a sequence you will change. Membership tests are O(n).

tuple

Ordered, immutable. Great for fixed records and as dictionary keys. Slightly lighter than a list.

set

Unordered, unique elements, fast O(1) membership tests. Reach for it to deduplicate or check containment.

dict

Key/value mapping with O(1) lookups, insertion-ordered since Python 3.7. The workhorse for lookups by name.

Rule of thumb

• Need order and changes? list.
• Need a constant record? tuple.
• Need uniqueness or fast membership? set.
• Need lookup by key? dict.