Lists: Ordered and Changeable

Scenario: A queue of services changes as incidents open and close.

New words, in plain English

• List - an ordered, mutable collection
• Mutable - able to change after creation
• Element - one value in a collection

Lists use square brackets. Index and slice them like strings. append, extend, insert, remove, pop, sort, and reverse modify a list; sorted returns a new list.

Analogy: A Python program is like a clear set of instructions for a careful helper: names label things, indentation groups steps, and errors explain where the helper became confused.

A small, real example

queue = ["api", "db"]
queue.append("cache")
finished = queue.pop(0)
print(finished, queue)

Tip: Copy with items.copy() or items[:] when two independent lists are required.

Goal: Practice this idea in the py-list-basics challenge at /labs/python. Fix the broken program, run it yourself, then use check to prove the real end state.