Combining Input and Output

Most useful programs need to communicate with the user — asking for data and reporting results. In Python this is done with input() and print().

The input() Function

input() displays a prompt string, waits for the user to type something and press Enter, and then returns what the user typed as a string:

>>> name = input("What is your name? ")
What is your name? Alice
>>> name
'Alice'
>>> type(name)
<class 'str'>

The result is always a string, regardless of what the user types.

Converting Input to Numbers

Since input() always returns a string, you must convert to a number if you need arithmetic. Use int() for integers or float() for decimal numbers:

>>> age_str = input("Enter your age: ")
Enter your age: 20
>>> age = int(age_str)
>>> age + 1
21

You can combine the two steps on one line, which is the most common pattern:

>>> age = int(input("Enter your age: "))
Enter your age: 20

>>> length = float(input("Enter room length: "))
Enter room length: 20.5
>>> type(length)
<class 'float'>

Warning

If the user types something that cannot be converted — for example, typing "abc" when you call int() — Python raises a ValueError and the program stops. We cover how to handle this gracefully in the While Loops chapter.

A Complete Input/Output Example

Here is a small program that reads two numbers and prints their sum:

a = float(input("Enter first number: "))
b = float(input("Enter second number: "))
print(f"The sum is {a + b}.")

Sample run:

Enter first number: 3.5
Enter second number: 1.5
The sum is 5.0.

Order Matters

The prompt string in input() is shown before reading, so the user sees what to type before entering a value.