When should I use list and when tuple?

The choice between mutable lists and immutable tuples in Python depends on the specific architectural task and data handling logic. Understanding these differences allows you to write more efficient, readable, and safe code, preventing accidental state modifications where it is not allowed.

Lists, denoted by square brackets, are created for situations where the contents of a collection need to change dynamically during program execution. You can add new elements, delete existing ones, sort them, or modify values on the fly. This is a universal tool for working with variable-length data sequences.

Tuples, denoted by parentheses, are immutable sequences, making them an ideal choice for storing fixed sets of data. If you know for sure that the composition of elements should not change after creation, using a tuple guarantees the integrity of this data and protects it from accidental overwriting in other parts of the program.

Due to their immutability, tuples have an important technical advantage — they are hashable objects, provided all their elements are also hashable. This allows them to be used as keys in dictionaries or as elements in sets, which is impossible with lists. In addition, tuples take up slightly less memory in the operating system and work a bit faster during creation and iteration.

Tuples are also extremely useful for returning multiple values from functions, acting as lightweight data packages. Unpacking such tuples into variables looks concise and clear, making the code more maintainable.