2.1 Creating and Accessing Lists

Example: Create a Python list of 24, 22, 5, 34, 81, and 10. Save the list to the variable name my_list and display it.

1. Click + Code to add a code-cell
2. Type my_list = [24,22,5,34,81,10]
3. Type my_list
4. Click play button

my_list = [24,22,5,34,81,10]
my_list

[24, 22, 5, 34, 81, 10]

Example: Create a list named x using the following integers: 10, 14, 20 and 15. Print the list.

x = [10,14,20,15]
x

[10, 14, 20, 15]

Example: Create a list named x using the following colors: red, yellow, green and blue. Print the list.

y = ['red','yellow','green','blue']  # string data in quotes
y

['red', 'yellow', 'green', 'blue']

List elements are indexed, and we can use the index operator to access its elements. The first element has index 0, the second element has index 1 etc.

Example: Create a list of 24, 22, 5, 34, 81 and 10. Save the list in x and display the entire list.

x = [24, 22, 5, 34, 81, 10]
x

[24, 22, 5, 34, 81, 10]

Example: From the list x above, display the first element. See code below.

x[0]

24

Example: From the list x above, display the third element. See code below.

x[2]

5

Example: From the list x above, display the last element?

1. Click + Code
2. Type x = [24,22,5,34,81,10]
3. Type x[-1]
4. Click play button

x = [24,22,5,34,81,10]

x[-1]

10

Note: The index for the last element of a list is $-1$, the second from the last is $-2$, the third from the last is $-3$, etc

Example: Create a list named z using the following items: Monday, Tuesday, Wednesday, 4, 5, 6, and 7.0. Here, we have string, integer and float data types.

z = ['Monday', 'Tuesday', 'Wednesday', 4, 5, 6, 7.0]

To display the whole list, enter its name or use the print function.

print(z)

['Monday', 'Tuesday', 'Wednesday', 4, 5, 6, 7.0]

z[0]      # the first item

'Monday'

z[-1]    # the last item

7.0

print(z[6])     # the 7 th item
print(z[-2])    # the second from the last

7.0
6

Note: To display multiple items of a Python list, use the slicing operator [a:b] from a to b-1. For example, z[0:3] will use index 0, 1, and 2. Notice 3 is not included.

Example: Display the first 3 elements of z.

print(z[0:3])

['Monday', 'Tuesday', 'Wednesday']

An Empty List

A list that contains no elements is called an empty list; you can create one with empty brackets,

x =

x=[]
x

[]

Lists are mutable

Elements of a list can be changed (replaced).

Example: From the list, x=[10,20,30], replace the second element, x[1]=20, with the letter a.

x = [10, 20, 30]
print(x)
x[1] = 'a'   # assign 'a' to the second element (replace 20 with 'a')
print(x)

[10, 20, 30]
[10, 'a', 30]

Adapted from Python for Introductory Statistics, by Simon Aman (Truman College, City Colleges of Chicago), licensed under CC BY 4.0. Changes were made: reformatted as an accessible XYZ web edition with live in-browser code cells. License: CC-BY-4.0.