← Python

len() function

len() returns the number of characters in a string (or items in a sequence)

What it does: 'Python' has 6 characters, so len() returns 6. The empty string has zero characters, so len('') returns 0. Count each character: H-e-l-l-o = 5. H-i = 2 characters. Count including the space: H-e-l-l-o-space-W-o-r-l-d = 11. A space is a character — len() counts everything between the quotes. A-l-i-c-e = 5 characters. len() returns a whole number — the count of characters.

Common mistakes: Line 2 is missing parentheses. Should be: length = len(name). Line 2 puts the variable in quotes. Should be: len(word).

Class: _____________________ · Name: _____________________ · Date: _________

Free printable worksheet with full answer key — or add this module to a journey and assign it to your class.

🖨 Print Worksheet and Answer key of len() function (PDF)

Take this worksheet further — free with Cloodit

Each concept is reinforced from every angle — learned, then applied, then tested.

Learning

Duo

What is len("Hello")?

Matches

❌ len(Hello)

↓

Error: Missing quotes

Applying

Meanings

Term

len("Hello")

Meaning

len() counts characters - len("Hello") gives 5.

Practice

length = len("Number of letters in this sentence.")

Testing

Gaps

length = ("Hello")

Check Answer

Spots

1name = "Alice"

2length = len name

Cloodit turns curriculum-aligned coding content into journeys students work through one biome at a time.

Students earn collectable badges

Over 100 of them, across seven natural biomes.

Study Buddy

Students build a real study resource

Turns their work into revision material ready for Flash Cards and Exam study.

Diamond Dash — one of Cloodit's live, competitive Sprint games

Students lock in with Sprints

Live, competitive practice for the start of the lesson or a teacher-led lesson finisher.

A Cloodit certificate of achievement, ready to personalise and print

Custom printable certificates

Honour your top performers, or encourage a student who's trying hard — ready to print in seconds.

Teach this with your class →

Quick Questions

1. What is len("Hello")?

A. 5 ✓

B. 6

Count each character: H-e-l-l-o = 5

2. What is len("Hi")?

A. 3

B. 2 ✓

H-i = 2 characters

3. What is len("Hello World")?

A. 11 ✓

B. 10

Count including the space: H-e-l-l-o-space-W-o-r-l-d = 11

4. Do spaces count in len()?

A. No

B. Yes ✓

A space is a character — len() counts everything between the quotes

5. After name = "Alice", what is len(name)?

A. 5 ✓

B. 4

A-l-i-c-e = 5 characters

Match the Pairs

len(Hello) → Error: Missing quotes

len('cat', 'dog') → Error: Too many arguments

n = len('Python') → Valid: n stores 6

len('') → Ok: Returns 0

print(len('Hello')) → Output: 5

w = 'cat' print(len(w)) → Output: 3

Key Term

len("Hello")

len() counts characters - len("Hello") gives 5.~~len("Hello World")

Fill in the Blanks

1. length = len("Hello")

2. name = "Alice" result = len(name) print(result)

3. message = "Hi there" size = len(message)

4. word = "Python" length = len(word) print(length)

5. text = "Hello World" count = len(text) print(count)

Spot the Error

Question 1

A name = "Alice"

B length = len name

C print(length)

Line B — Line 2 is missing parentheses. Should be: length = len(name)

Question 2

A word = "Python"

B size = len("word")

C print(size)

Line B — Line 2 puts the variable in quotes. Should be: len(word)

Question 3

A message = "Hello"

B count = length(message)

C print(count)

Line B — Line 2 uses the wrong function name. Should be: len(message)

Question 4

A text = "Hi there"

B size = len(text)

C print(size)

D new_len = len(Hello)

E print(new_len)

Line D — Line 4 is missing quotes around Hello. Should be: len("Hello")

Question 5

A name = "Bob"

B name_length = len(name)

C message = "Python Code"

D msg_len = len message

E print(msg_len)

Line D — Line 4 is missing parentheses. Should be: msg_len = len(message)

For Teachers

Create a free class, add this module to a journey, and track who's stuck.

Create a free teacher account →

No credit card. No setup fee. Make a class and invite students in under three minutes.

For Students

Practice this topic interactively, track progress, and unlock badges.

Start Learning Free →

Have a class code?