Length and iteration methods in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the len() function do in Python?

The len() function returns the number of items in an object like a list, string, tuple, or dictionary.

beginner

How can you loop through each item in a list named fruits?

Use a for loop: <br>for fruit in fruits:<br>   print(fruit) This goes through each item one by one.

intermediate

What is the difference between for and while loops?

for loops run a set number of times over a sequence. while loops run as long as a condition is true.

beginner

How do you find the length of a string name = 'Alice'?

Use len(name). It will return 5 because 'Alice' has 5 characters.

intermediate

What happens if you try to use len() on an integer like len(5)?

You get a TypeError because integers don’t have a length. len() works only on collections like strings, lists, or tuples.

What does len([1, 2, 3, 4]) return?

A 4

B 3

C 1

D Error

len() counts the number of items in the list, which is 4.

Which loop is best to use when you know exactly how many times to repeat?

A while loop

B try-except block

C if statement

D for loop

for loops are ideal for repeating a fixed number of times over a sequence.

What will this code print?<br>for i in range(3):<br>   print(i)

A 1 2 3

B 0 1 2

C 3 2 1

D Error

range(3) generates numbers 0, 1, 2. The loop prints each number.

What does len('hello') return?

A 6

B 4

C 5

D Error

The string 'hello' has 5 characters, so len() returns 5.

Which of these can you use len() on?

A List

B Integer

C Float

D Boolean

len() works on collections like lists, strings, tuples, but not on single numbers or booleans.

Explain how to find the length of a list and how to loop through its items.

Think about counting items and visiting each one.

Describe the difference between a for loop and a while loop with examples.

One repeats over a sequence, the other repeats while a condition is true.