List mutability in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean that lists in Python are mutable?

It means you can change, add, or remove items in a list after it is created without making a new list.

beginner

Which of these operations changes a list in place?

my_list = [1, 2, 3]

Operations like my_list.append(4) or my_list[0] = 10 change the list without creating a new one.

intermediate

What happens if you assign a new list to a variable that held a list before?

The variable now points to a new list. The old list stays unchanged unless other variables also point to it.

beginner

True or False: Strings in Python are mutable like lists.

False. Strings are immutable, meaning you cannot change them after creation, unlike lists.

intermediate

How does list mutability affect function arguments when you pass a list?

If you change the list inside the function, the change affects the original list outside the function because both refer to the same list.

Which method changes a list by adding an item at the end?

A replace()

B append()

C insert_at_end()

D add()

The append() method adds an item to the end of a list. The others are not valid list methods.

What will this code print?

lst = [1, 2, 3]
lst[1] = 5
print(lst)

A [1, 2, 3]

B Error

C [5, 2, 3]

D [1, 5, 3]

Changing lst[1] to 5 updates the second item. Lists are mutable, so the change is allowed.

If you do new_list = old_list and then change new_list, what happens to old_list?

A old_list changes too

B old_list stays the same

C old_list is deleted

D Error

Both variables point to the same list, so changes via new_list affect old_list.

Which of these types is immutable in Python?

A list

B dictionary

C string

D set

Strings cannot be changed after creation, unlike lists, dictionaries, and sets.

What does mutability allow you to do with a list?

A Change its contents without making a new list

B Prevent any changes to the list

C Make the list read-only

D Convert the list to a string automatically

Mutability means you can change the list's contents directly.

Explain what list mutability means and give an example of changing a list item.

Think about how you can change a list after you create it.

Describe how passing a list to a function can lead to changes outside the function.

Consider what happens if you add or remove items inside the function.