COLLECTIONSChapter 5 · Collections

List methods

Lists change in place with methods: .append(x) adds to the end, .insert(i, x) adds at a position, .remove(x) deletes the first match, .pop() removes and returns the last item, and .sort() puts the list in order. sorted(items) returns a new sorted list and leaves the original alone. x in items checks membership and items.index(x) finds a position.

Worked example

How it reads

.append, .insert, .remove and .pop change the list itself
.pop() also hands back the item it removed
sorted(planets) makes a new list, planets.sort() reorders the original

Common mistakes

planets = planets.sort() sets planets to None: .sort() changes the list and returns nothing.
.remove(x) raises ValueError when x is not in the list. Check with in first.

Cloud tip: Reach for sorted() when you still need the original order later, and .sort() when you do not.