Iterating over lists in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean to iterate over a list in Python?

Iterating over a list means going through each item in the list one by one to perform an action with each item.

beginner

Which Python keyword is commonly used to loop through each item in a list?

The for keyword is used to loop through each item in a list.

beginner

What will this code print?<br>

fruits = ['apple', 'banana', 'cherry']
for fruit in fruits:
    print(fruit)

It will print each fruit on its own line:<br>apple<br>banana<br>cherry

intermediate

How can you access both the index and the item when iterating over a list?

Use the enumerate() function in the loop, like:<br>

for index, item in enumerate(my_list):
    # do something with index and item

intermediate

True or False: You can modify the items of a list directly while iterating over it.

True, but you should be careful. Modifying the list while iterating can cause unexpected behavior if you add or remove items. Changing item values is safe.

What does the following code do?<br>

numbers = [1, 2, 3]
for num in numbers:
    print(num * 2)

A Causes an error

B Prints 1, 2, 3 each on a new line

C Prints 2, 4, 6 each on a new line

D Prints the list [2, 4, 6]

The loop goes through each number and prints the number multiplied by 2.

Which function helps get the index and value when looping over a list?

A enumerate()

B index()

C range()

D len()

The enumerate() function returns pairs of (index, value) during iteration.

What will this code print?<br>

items = ['a', 'b', 'c']
for i in range(len(items)):
    print(items[i])

A 0 1 2 on separate lines

B a b c on separate lines

C Error because of range()

D Nothing

The loop uses indexes to access each item and prints them one by one.

Is this a correct way to loop over a list?<br>

for item in my_list:
    print(item)

A Only works if list has numbers

B No, it will cause an error

C Only works if list is empty

D Yes, it loops through each item

This is the standard way to loop through all items in a list.

What happens if you modify a list by adding items while iterating over it?

A It can cause unexpected behavior or an infinite loop

B The loop will include the new items automatically

C Python prevents adding items during iteration

D Nothing special happens

Changing the list size during iteration can confuse the loop and cause errors or infinite loops.

Explain how to use a for loop to iterate over a list and print each item.

Think about how you would tell a friend to read each item one by one.

Describe how to get both the index and the value of items when looping over a list.

Remember there is a special function that helps with indexes.