User Input

So far, every program has worked with values written into the code. Real programs respond to the people using them. The input() function lets your program ask a question and wait for an answer.

Asking a question

input() shows a prompt, waits for the user to type something and press Enter, then gives back what they typed.

Run this and type your answer in the Output panel:

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

Output

Tip: End your prompt with a space, as in "What is your name? ", so the user's answer doesn't run into the question.

Input is always a string

Whatever the user types, input() returns a string, even if it looks like a number. Run this and type 5:

answer = input("Type a number: ")
print(type(answer))
print(answer * 3)

Output

You got 555, not 15, because "5" * 3 repeats the text. To do maths, convert the input first:

answer = input("Type a number: ")
number = int(answer)
print(number * 3)

Output

You can convert in one step by wrapping input() in int() or float():

age = int(input("How old are you? "))
height = float(input("How tall are you in metres? "))

print(f"Next year you will be {age + 1}.")
print(f"That's {height * 100:.0f} cm.")

Output

Use int() for whole numbers and float() when the user might type a decimal.

When the input isn't a number

If the user types something that can't be converted, Python raises a ValueError. Run this and type hello:

number = int(input("Type a whole number: "))
print(number * 2)

Output

You'll learn how to handle errors like this gracefully in the Errors and Exceptions lesson. For now, just know why it happens.

Going deeper: Why int("3.5") fails optional

int() can turn a decimal number into a whole number, but it can't turn decimal text into one. The text "3.5" isn't a whole number, so int() refuses:

print(int(3.5))      # a float: works, gives 3
print(int("3.5"))    # text with a decimal point: ValueError

Output

If the user might type a decimal but you need a whole number, convert to float first, then to int:

answer = input("How many hours did you work? ")
hours = int(float(answer))
print(f"Full hours: {hours}")

Output

Remember that int() cuts off the decimals rather than rounding. Use round(float(answer)) if you want 3.7 to become 4.

Cleaning up text input

People add stray spaces and capital letters. Combine input() with the string methods from the last lesson to tidy things up:

color = input("What's your favourite colour? ").strip().lower()
print(f"You chose: {color}")

Output

Going deeper: Reading several values from one line optional

split() from the String Methods lesson lets you read several values the user types on one line. Run this and type something like 3 4:

line = input("Enter width and height separated by a space: ")
parts = line.split()

width = int(parts[0])
height = int(parts[1])
print(f"Area: {width * height}")

Output

Putting it together: a tip calculator

bill = float(input("Bill amount: "))
tip_percent = int(input("Tip percentage (e.g. 15): "))
people = int(input("Number of people: "))

tip = bill * tip_percent / 100
total = bill + tip
each = total / people

print(f"Tip: {tip:.2f}")
print(f"Total: {total:.2f}")
print(f"Each person pays: {each:.2f}")

Output

Exercises

These exercises are interactive. Your program asks questions, and you type the answers in the Output panel.

Exercise 1: Personal greeting

Ask the user for their name and their city, then print Hello <name> from <city>!

# Ask for name and city, then greet the user

Output

Exercise 2: Add two numbers

Ask for two whole numbers and print their sum. If the user types 4 and 6, it should print 4 + 6 = 10.

# Ask for two numbers and print their sum

Output

Exercise 3: Temperature converter

Ask for a temperature in Celsius (it may have decimals) and print it in Fahrenheit using F = C × 9 / 5 + 32. For 25, print 25.0°C is 77.0°F.

# Convert Celsius to Fahrenheit

Output

Exercise 4: Fix the program

This program is meant to tell the user how old they'll be in 10 years, but it crashes. Run it, read the error, and fix it.

age = input("How old are you? ")
print(f"In 10 years you will be {age + 10}.")

Output

Summary

input("prompt ") waits for the user and returns what they typed.
The result is always a string. Convert it with int() or float() before doing maths.
Converting text that isn't a number raises a ValueError.
Chain .strip() and .lower() to clean up text input.
split() lets you read several values from one line.