List length and membership test in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

How do you find the number of items in a list in Python?

Use the len() function. For example, len(my_list) returns the number of items in my_list.

beginner

What does the expression item in my_list check?

It checks if item is present anywhere inside my_list. It returns True if found, otherwise False.

beginner

What will len([]) return?

It returns 0 because the list is empty and has no items.

beginner

How can you check if the number 5 is NOT in a list called numbers?

Use the expression 5 not in numbers. It returns True if 5 is not found in the list.

beginner

What is the output of this code?

my_list = [1, 2, 3, 4]
print(len(my_list))
print(3 in my_list)
print(5 in my_list)

The output is:

4
True
False

Explanation:
- len(my_list) is 4 because there are 4 items.
- 3 in my_list is True because 3 is in the list.
- 5 in my_list is False because 5 is not in the list.

What does len([10, 20, 30]) return?

A 3

B 30

C 0

D Error

The list has 3 items, so len() returns 3.

Which expression checks if 'apple' is in the list fruits?

A 'apple' not in fruits

B fruits in 'apple'

C 'apple' in fruits

D len('apple') in fruits

The correct syntax to check membership is item in list.

What will len([]) output?

A 1

B 0

C None

D Error

An empty list has zero items, so len([]) returns 0.

What does 7 not in [1, 2, 3, 4] return?

A True

B False

C 7

D Error

Since 7 is not in the list, the expression returns True.

If my_list = ['a', 'b', 'c'], what is 'd' in my_list?

A Error

B True

C 'd'

D False

'd' is not in the list, so the expression returns False.

Explain how to find the length of a list and check if an item is inside it in Python.

Think about how you count items and how you ask if something is present.

Describe what happens when you use not in with a list.

It's like asking if something is missing.