List methods and functions

Some built-in functions work on lists: len(); list(), which makes an empty list or turns a sequence into a list (list('abc') gives ['a', 'b', 'c']); and min(), max() and sum().

List methods that add elements:

• append(x) adds one element at the end. If x is itself a list, it is added as one element: [1, 2].append([3, 4]) makes [1, 2, [3, 4]].
• extend(list2) adds each element of list2 at the end: [1, 2].extend([3, 4]) makes [1, 2, 3, 4].
• insert(i, x) puts x at index i, moving the rest along.

Methods that find or remove elements:

• count(x): how many times x occurs.
• index(x): the position of the first x; a ValueError if x is not there. For [7, 3, 7], index(7) is 0.
• remove(x): deletes the first x only (ValueError if absent).
• pop(i): deletes the element at index i and returns it; with no index, it removes the last element.

Methods that rearrange:

• reverse() reverses the list in place.
• sort() sorts it in place; sort(reverse = True) sorts it in descending order.

Compare these with the function sorted(list1), which returns a new sorted list and leaves list1 unchanged.