Changing Lists

Lesson

Changing Lists

Lists can be changed after creation.

Assigning to an index replaces that element:

colors = ["red", "green", "blue"]
colors[1] = "yellow"
print(colors)

Output:

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

append adds an element at the end. It is called with a dot on the list itself — this form is called a method:

colors.append("black")
print(colors)

Output:

['red', 'yellow', 'blue', 'black']

insert places an element at a given index, pushing later elements one step right:

colors.insert(0, "white")
print(colors)

Output:

['white', 'red', 'yellow', 'blue', 'black']

Exercise

The starter code creates guests with two names.

Append "Alan".
Replace the first element with "Edsger".
Insert "Barbara" at index 1.
Print guests. The final list is ['Edsger', 'Barbara', 'Grace', 'Alan'].

Run your code to see the output, then press Submit.

Tests

import unittest


class TestChangingLists(unittest.TestCase):
    def test_final_list_is_correct(self):
        self.assertEqual(guests, ["Edsger", "Barbara", "Grace", "Alan"])

Solution

guests = ["Ada", "Grace"]

guests.append("Alan")
guests[0] = "Edsger"
guests.insert(1, "Barbara")

print(guests)

Solution hidden. Give it a real try first.

Discussion

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main.py

Console

Press Run to execute your code, or Submit to test and complete this problem.