Ordered collections.
WHAT A LIST IS
An ordered collection you can change.
WHAT YOU DO WITH THEM
Add items Remove items Access by position Iterate over them Sort them Check membership
POSITIONS START AT ZERO
The first item is at position zero.
The most common source of errors for beginners.
NEGATIVE POSITIONS
Count from the end, which is frequently convenient.
SLICING
Taking a portion of a list by range.
Extremely useful and worth learning properly.
WHAT TO BE CAREFUL WITH
Modifying a list while iterating over it, which produces surprising results Assuming a list is sorted Very large lists held entirely in memory
WHAT TO USE INSTEAD OF A LIST
A set, when you only check membership and uniqueness matters A dictionary, when you look items up by key
WHY
Both are far faster for those purposes on large collections.
WHAT TUPLES ARE FOR
Collections that must not change, and as dictionary keys.
