Python Lesson 3: input(), int(), float() and Data Types

A complete lesson · 60 minutes

Teach it, see it, practise it, all on this page.

Open this page with your learner and work down it, or press Teach this lesson to go through it one step at a time on a big screen. Every section has something to do.

See the teacher's plan

Warm-up4 min
Asking a question7 min
Text or number?9 min
Convert straight away8 min
Calculators7 min
Age in 20408 min
Pizza planner8 min
Story machine5 min
Quiz3 min
Set the project1 min

By the end you can

Ask a question with input() and store the answer
Explain why input() always gives text
Convert with int(), float() and str()
Build calculators and planners that work for any input

Before you start

Session 2: variables and f-strings

Have ready

This page (type answers in the Input box under each editor, one per line)

Beginner · ages 10 and up

Warm-up · think first

A form asks "How old are you?" and you type 11. Then it asks "How old will you be in 5 years?" Can the computer add 5 to what you typed straight away? What might go wrong?

Show the answer

What you type arrives as text, like a word. Adding 5 to the word "11" makes no sense, so the program must first turn the text into a number.

Teacher tip: Write "11" and 11 on paper: which is a word made of characters, and which is a number you can add to?

Part 1 of 4 · learn, see, practise

Asking a question

input("question") shows the question, waits for an answer and gives it back. Store it in a variable.

On this page, type answers in the Input box, one per line, then press Run. The program takes the next line each time it asks.

Example: run it, then change it

name = input("What is your name? ")
print(f"Hello, {name}! Nice to meet you.")

name = input("What is your name? ")
print(f"Hello, {name}! Nice to meet you.")

Input: one answer per line, used when the program asks

Output

What is your name? Asha
Hello, Asha! Nice to meet you.

Memory boxes

name'Asha'str

Change Asha to your name and run again.

Practise it

Start with the warm-up and go as far as you can. The stretch questions are meant to be hard.

Warm-up

1.1 Ask for a name and print Welcome, <name>!

Task 1.1

Input: one answer per line, used when the program asks

Output

(nothing is printed)

Memory boxes

No variables yet

Model answer (for the teacher)

name = input("Name? ")
print(f"Welcome, {name}!")

Core

1.2 Ask for a colour, then an animal. Print: Your <colour> <animal> is ready.

Task 1.2

Input: one answer per line, used when the program asks

Output

(nothing is printed)

Memory boxes

No variables yet

Model answer (for the teacher)

c = input("Colour? ")
a = input("Animal? ")
print(f"Your {c} {a} is ready.")

Stretch 🔥

1.3 Ask for three words, then print them in reverse order on one line, separated by spaces.

Task 1.3

Input: one answer per line, used when the program asks

Output

(nothing is printed)

Memory boxes

No variables yet

Model answer (for the teacher)

a = input("1? ")
b = input("2? ")
c = input("3? ")
print(c, b, a)

Part 2 of 4 · learn, see, practise

input() always gives text

input() gives back a string even if digits are typed. "11" + "5" is "115".

int("11") makes the whole number 11; float("2.5") makes a decimal number; str(11) makes text again.

Example: run it, then change it

a = input("First number: ")
b = input("Second number: ")
print("Joined as text:", a + b)
print("Added as numbers:", int(a) + int(b))

a = input("First number: ")
b = input("Second number: ")
print("Joined as text:", a + b)
print("Added as numbers:", int(a) + int(b))

Input: one answer per line, used when the program asks

Output

First number: 11
Second number: 5
Joined as text: 115
Added as numbers: 16

Memory boxes

a'11'strb'5'str

Same answers, very different results.

Practise it

Start with the warm-up and go as far as you can. The stretch questions are meant to be hard.

Warm-up

2.1 Read two numbers and print their sum as the last line.

Task 2.1

Input: one answer per line, used when the program asks

Output

(nothing is printed)

Memory boxes

No variables yet

Model answer (for the teacher)

a = int(input("a? "))
b = int(input("b? "))
print(a + b)

Core

2.2 Read a whole number n. Print n joined with itself as text, then n doubled as a number, on the last two lines (for 5: 55 then 10).

Task 2.2

Input: one answer per line, used when the program asks

Output

(nothing is printed)

Memory boxes

No variables yet

Model answer (for the teacher)

n = input("n? ")
print(n + n)
print(int(n) * 2)

Stretch 🔥

2.3 Read the side of a square. Print Area: … and Perimeter: … as the last two lines.

Task 2.3

Input: one answer per line, used when the program asks

Output

(nothing is printed)

Memory boxes

No variables yet

Model answer (for the teacher)

s = int(input("Side? "))
print(f"Area: {s * s}")
print(f"Perimeter: {4 * s}")

Part 3 of 4 · learn, see, practise

Convert straight away

Convert as you read: age = int(input("Age? ")). Use int for whole numbers and float for anything with a decimal point.

If someone types a word where a number is expected, int() stops with a ValueError.

Example: run it, then change it

age = int(input("How old are you? "))
print(f"In 5 years you will be {age + 5}.")
height = float(input("Your height in metres? "))
print(f"Twice your height is {height * 2} m.")

age = int(input("How old are you? "))
print(f"In 5 years you will be {age + 5}.")
height = float(input("Your height in metres? "))
print(f"Twice your height is {height * 2} m.")

Input: one answer per line, used when the program asks

Output

How old are you? 11
In 5 years you will be 16.
Your height in metres? 1.45
Twice your height is 2.9 m.

Memory boxes

age11intheight1.45float

Look at the memory boxes: age is an int, height a float.

Practise it

Start with the warm-up and go as far as you can. The stretch questions are meant to be hard.

Warm-up

3.1 Read an age and print: Next year you will be <age + 1>.

Task 3.1

Input: one answer per line, used when the program asks

Output

(nothing is printed)

Memory boxes

No variables yet

Model answer (for the teacher)

age = int(input("Age? "))
print(f"Next year you will be {age + 1}.")

Core

3.2 Read a price (decimal) and a quantity (whole). Print Total: and the cost.

Task 3.2

Input: one answer per line, used when the program asks

Output

(nothing is printed)

Memory boxes

No variables yet

Model answer (for the teacher)

p = float(input("Price? "))
q = int(input("Qty? "))
print(f"Total: {p * q}")

Stretch 🔥

3.3 Read a temperature in °C and print it in °F (F = C × 9 / 5 + 32) as the last line, just the number.

Task 3.3

Input: one answer per line, used when the program asks

Output

(nothing is printed)

Memory boxes

No variables yet

Model answer (for the teacher)

c = float(input("C? "))
print(c * 9 / 5 + 32)

Part 4 of 4 · learn, see, practise

Calculators that work for anyone

Put it together: read, convert, calculate, print. The program has no numbers of its own any more: it works for whatever is typed.

Example: run it, then change it

a = float(input("First number: "))
b = float(input("Second number: "))
print(f"{a} + {b} = {a + b}")
print(f"{a} x {b} = {a * b}")
print(f"{a} / {b} = {a / b}")

a = float(input("First number: "))
b = float(input("Second number: "))
print(f"{a} + {b} = {a + b}")
print(f"{a} x {b} = {a * b}")
print(f"{a} / {b} = {a / b}")

Input: one answer per line, used when the program asks

Output

First number: 7
Second number: 2
7.0 + 2.0 = 9.0
7.0 x 2.0 = 14.0
7.0 / 2.0 = 3.5

Memory boxes

a7.0floatb2.0float

Try other numbers. What happens with 0 as the second number?

Practise it

Start with the warm-up and go as far as you can. The stretch questions are meant to be hard.

Warm-up

4.1 Read two whole numbers and print their product as the last line.

Task 4.1

Input: one answer per line, used when the program asks

Output

(nothing is printed)

Memory boxes

No variables yet

Model answer (for the teacher)

a = int(input())
b = int(input())
print(a * b)

Core

4.2 Read a bill and the number of people. Print Each pays: and the share.

Task 4.2

Input: one answer per line, used when the program asks

Output

(nothing is printed)

Memory boxes

No variables yet

Model answer (for the teacher)

bill = float(input("Bill? "))
n = int(input("People? "))
print(f"Each pays: {bill / n}")

Stretch 🔥

4.3 Read a number of seconds and print it as minutes and seconds, like 2 min 10 sec, as the last line.

Task 4.3

Input: one answer per line, used when the program asks

Output

(nothing is printed)

Memory boxes

No variables yet

Model answer (for the teacher)

s = int(input("Seconds? "))
print(f"{s // 60} min {s % 60} sec")

Watch out

Common mistakes

Adding text

"3" + "4" is "34". Convert with int() or float() first.

Converting too late

Convert once when you read the value.

Missing a bracket

int(input("Age? ") is missing a closing bracket: two opened, two closed.

Class activity 1 of 3

Age in the year 2040

Ask for a name and a birth year. The last two lines must be: Hi <name>! and In 2040 you will be <age>.

Read the name.
Read the birth year and convert it with int().
Work out age = 2040 - year.
Print the two lines with f-strings.

Your code

name = input("Your name? ")
year = input("Year you were born? ")

# Step 2: convert year

# Step 3: work out the age

# Step 4: print two lines

name = input("Your name? ")
year = input("Year you were born? ")

# Step 2: convert year

# Step 3: work out the age

# Step 4: print two lines

Input: one answer per line, used when the program asks

Output

Your name? Asha
Year you were born? 2014

Memory boxes

name'Asha'stryear'2014'str

Hint

year = int(input(...))

Model answer (for the teacher)

name = input("Your name? ")
year = int(input("Year you were born? "))
age = 2040 - year
print(f"Hi {name}!")
print(f"In 2040 you will be {age}.")

Class activity 2 of 3

Pizza party planner

Read the number of guests and how many slices each eats. A pizza has 8 slices. The last three lines must be: Slices: …, Pizzas: … (enough pizzas, rounded up) and Spare slices: ….

Read guests and slices each, as whole numbers.
slices = guests × slices each.
pizzas = (slices + 7) // 8 rounds up to whole pizzas.
spare = pizzas × 8 - slices.
Print the three lines.

Your code

guests = int(input("Guests? "))
each = int(input("Slices each? "))

# Step 2

# Step 3

# Step 4

# Step 5

guests = int(input("Guests? "))
each = int(input("Slices each? "))

# Step 2

# Step 3

# Step 4

# Step 5

Input: one answer per line, used when the program asks

Output

Guests? 10
Slices each? 3

Memory boxes

guests10inteach3int

Hint

For 30 slices: (30 + 7) // 8 = 4 pizzas.

Model answer (for the teacher)

guests = int(input("Guests? "))
each = int(input("Slices each? "))
slices = guests * each
pizzas = (slices + 7) // 8
spare = pizzas * 8 - slices
print(f"Slices: {slices}")
print(f"Pizzas: {pizzas}")
print(f"Spare slices: {spare}")

Class activity 3 of 3

Story machine

Read a name, an animal, a place and a food. Print a story of at least three lines. The first story line must be exactly: Once upon a time, <name> the <animal> lived on <place>.

Read the four words.
Print the first line exactly as shown, with an f-string.
Add at least two more lines that use the place and the food.
Run it with silly words and read it aloud!

Your code

name = input("A name? ")
animal = input("An animal? ")
place = input("A place? ")
food = input("A food? ")

# Step 2: the first line

# Step 3: two more lines

name = input("A name? ")
animal = input("An animal? ")
place = input("A place? ")
food = input("A food? ")

# Step 2: the first line

# Step 3: two more lines

Input: one answer per line, used when the program asks

Output

A name? Zoe
An animal? tiger
A place? Mars
A food? pizza

Memory boxes

name'Zoe'stranimal'tiger'strplace'Mars'strfood'pizza'str

Hint

The four questions print four lines first, so the story starts on line 5.

Model answer (for the teacher)

name = input("A name? ")
animal = input("An animal? ")
place = input("A place? ")
food = input("A food? ")
print(f"Once upon a time, {name} the {animal} lived on {place}.")
print(f"Every day {name} ate {food} for breakfast.")
print(f"One day the {food} ran out on {place}...")

Quiz · 8 questions

Check what you learned

Pick an answer to see if it is right and why. Your best score is saved on this device.

1What does this show?

print("7" + "3")

Show the answer

73. Two strings joined.

2What does this show?

print(int("7") + 3)

Show the answer

10. int("7") is the number 7.

3What does this show?

print(str(5) + "5")

Show the answer

55. str(5) is text.

4What does this show?

print(float("2.5") * 2)

Show the answer

5.0. A float answer: 5.0.

5What does this show?

print(int(3.9))

Show the answer

3. int() cuts off the decimal part.

6What does input() give back?

Show the answer

Always text (a string). Convert it when you need a number.

7Which line reads a whole number?

Show the answer

n = int(input("n? ")). Read with input, convert with int.

8What does this show?

print("3" * 3)

Show the answer

333. A string times a number repeats it.

After class · project

Unit converter

Build a converter that asks for kilometres and °C and converts them to miles and °F, then add a converter of your own.

Read kilometres with float(input(...)).
Miles = km × 0.621371.
Read °C; °F = °C × 9 / 5 + 32.
Add your own converter.
Print every answer as a sentence with units.

What to make: A program that asks at least three questions and prints at least three conversions.

Stretch: Use round(miles, 2) to show two decimal places.

How it is marked

Look for	Done well when
Input	Every value is read and converted
Formulas	All conversions are correct
Clear output	Each answer is a sentence with units
Own idea	One extra converter

Starter code to take home

Press Copy and paste it into the editor at home, or work on it right here.

Project starter

# ===== Unit converter =====
km = float(input("Distance in km: "))
miles = km * 0.621371
print(f"{km} km is {miles} miles")

# Temperature: read Celsius, print Fahrenheit

# Your own converter

# ===== Unit converter =====
km = float(input("Distance in km: "))
miles = km * 0.621371
print(f"{km} km is {miles} miles")

# Temperature: read Celsius, print Fahrenheit

# Your own converter

Input: one answer per line, used when the program asks

Output

Distance in km: Line 2: EOFError: EOF when reading a line (there is no more input; add lines to the Input box)

Memory boxes

No variables yet

Homework

Practise at home

Each one checks itself. Or print the practice sheet.

Warm-up

1. Read a number and print its square as the last line.

Homework 1

Input: one answer per line, used when the program asks

Output

(nothing is printed)

Memory boxes

No variables yet

Core

2. Read the length and width of a room (decimals allowed) and print the area as the last line.

Homework 2

Input: one answer per line, used when the program asks

Output

(nothing is printed)

Memory boxes

No variables yet

Stretch 🔥

3. Read the marks of three tests. Print the total and then the average, as the last two lines.

Homework 3

Input: one answer per line, used when the program asks

Output

(nothing is printed)

Memory boxes

No variables yet

For parents and teachers

The 60-minute lesson plan

Use it as it is, or stretch any part over two sessions. Each row links to the part of the page you need.

Time	Part	The teacher	The learner
0–4 min	Warm-up	"11" vs 11 on paper.	Explain the difference.
4–11 min	Asking a question	Show the Input box.	Reverse-words stretch.
11–20 min	Text or number?	Joined vs added.	Square area stretch.
20–28 min	Convert straight away	Make a ValueError happen.	Temperature stretch.
28–35 min	Calculators	Ask about dividing by 0.	Seconds stretch.
35–43 min	Age in 2040	Watch them use the Input box.	Pass all checks.
43–51 min	Pizza planner	Discuss rounding up.	Pass all checks.
51–56 min	Story machine	Read stories aloud.	Write a story.
56–59 min	Quiz	Run the quiz.	Answer.
59–60 min	Set the project	Open the converter starter.	Choose an extra converter.

Questions to ask

Why does "11" + "5" give 115?
When do you use float() instead of int()?
How do you round up a division to whole pizzas?

If it feels hard

Use paper cards for "11" and 11 and physically join or add them.

If it feels easy

Build a tip calculator: bill and tip percent in, tip and total out.

FAQ

Talking to the user: input() and types: questions

Why does Python input() return a string?

The keyboard sends characters, so input gives text and you convert it with int() or float().

How do I read a number from the user in Python?

Wrap input in int() or float(): age = int(input("Age? ")).

How does the Input box work on this page?

Each line is one answer, used in order whenever the program asks.

Talking to the user: input() and types

Teach it, see it, practise it, all on this page.

By the end you can

Before you start

Have ready

A form asks "How old are you?" and you type 11. Then it asks "How old will you be in 5 years?" Can the computer add 5 to what you typed straight away? What might go wrong?

Asking a question

Practise it

input() always gives text

Practise it

Convert straight away

Practise it

Calculators that work for anyone

Practise it

Common mistakes

Adding text

Converting too late

Missing a bracket

Age in the year 2040

Pizza party planner

Story machine

Check what you learned

Unit converter

How it is marked

Starter code to take home

Practise at home

The 60-minute lesson plan

Questions to ask

If it feels hard

If it feels easy

Talking to the user: input() and types: questions

Want a teacher to take this class?