### Data structures – Lists

A list is a sequence of variable length. Lists can be modified and items can be added and removed from the list.

A list is defined as a sequence of objects separated as commas and enclosed in []

An empty list can be defined with []

Examples

mylist = [1,2,3,4,5]

Operations on lists

+ concatenates the elements of two lists

* repeats the elements of a list

[] is also used to select items from a list

Examples

[1,2] + [3,4] results in [1,2,3,4]

2 * [1,2] results in [1,2,1,2]

t = [1,2,3,4]

t [1] is 2

t [1: 3] is [2,3,4]

t [2:] is [2,3,4]

t [: 3] is [1,2,3]

Operations on tuples also apply to lists.

The range (i, f, step) operation creates a list of numbers from start to end from step to step.

If i is omitted it is worth 0, if step is omitted it is worth 1

Example

range (2) is [1,2]

range (5.7) is [5,6,7]

range (8,12,2) is [8,10,12]

List methods

append (e) – add an element to the end of the list

extend (l) – add a list at the end

insert (i, n) – insert an element at position n-1

pop (n) – extract and return element n from the list

remove (n) – remove item n from the list

reverse () – invert the list items

count (e) – returns the number of times e appears in the list

index (e) – returns the position of the first occurrence of e in a list