Learn Without Walls
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Getting User Input with input()

What You'll Learn

1. The input() Function

input(): A built-in function that pauses your program, displays an optional prompt message, waits for the user to type something and press Enter, then returns whatever they typed as a string. 
name = input("What is your name? ")
print("Hello,", name + "!")
What is your name? Alice
Hello, Alice!

When Python encounters input(), it:

  1. Displays the prompt text (if provided)
  2. Pauses and waits for the user to type
  3. When the user presses Enter, returns what they typed as a string
  4. Stores the result in the variable
Important: Always include a space at the end of your prompt text (e.g., "Enter name: " not "Enter name:") so the user's typing does not bump against the prompt.

2. input() Always Returns a String

This is the most important thing to remember about input(): it always returns a string, even if the user types a number.

age = input("Enter your age: ")
print(type(age))
print(age)
Enter your age: 25
<class 'str'>
25

Even though the user typed 25, Python stores it as the string "25", not the number 25. This means you cannot do math with it directly:

age = input("Enter your age: ")
# This would cause an error!
# next_year = age + 1   # TypeError: can't add str and int
Common Beginner Mistake: Forgetting to convert input() results to numbers before doing math. This is one of the most common errors beginners encounter!

3. Converting Input to Numbers

To do math with user input, wrap the input() call with int() or float():

# For whole numbers, use int()
age = int(input("Enter your age: "))
next_year = age + 1
print("Next year you will be", next_year)

# For decimal numbers, use float()
price = float(input("Enter the price: $"))
tax = price * 0.09
print("Tax:", tax)
Enter your age: 25
Next year you will be 26
Enter the price: $19.99
Tax: 1.7991

Two Approaches to Converting

# Approach 1: Convert immediately (most common)
age = int(input("Age: "))

# Approach 2: Get input first, then convert
age_text = input("Age: ")
age = int(age_text)

Both approaches work. Approach 1 is more concise and is the standard pattern.

4. Building Interactive Programs

Simple Calculator

num1 = float(input("Enter first number: "))
num2 = float(input("Enter second number: "))

print("Sum:", num1 + num2)
print("Difference:", num1 - num2)
print("Product:", num1 * num2)
print("Quotient:", num1 / num2)
Enter first number: 10
Enter second number: 3
Sum: 13.0
Difference: 7.0
Product: 30.0
Quotient: 3.3333333333333335

Personalized Greeting

name = input("What is your name? ")
color = input("What is your favorite color? ")
food = input("What is your favorite food? ")

print()
print("Nice to meet you,", name + "!")
print("I hear you love", color, "and", food + ".")
What is your name? Alex
What is your favorite color? blue
What is your favorite food? pizza

Nice to meet you, Alex!
I hear you love blue and pizza.

5. Common Input Patterns

Getting Multiple Inputs for a Calculation

# Tip calculator
bill = float(input("Enter the bill amount: $"))
tip_percent = float(input("Tip percentage (e.g., 15, 20): "))

tip_amount = bill * (tip_percent / 100)
total = bill + tip_amount

print("Tip: $" + str(round(tip_amount, 2)))
print("Total: $" + str(round(total, 2)))
Enter the bill amount: $45.50
Tip percentage (e.g., 15, 20): 20
Tip: $9.1
Total: $54.6

6. What Happens When Input Goes Wrong

If the user types something that cannot be converted, Python will raise a ValueError:

# If the user types "abc" when asked for a number:
age = int(input("Enter your age: "))
# User types "abc"
# ValueError: invalid literal for int() with base 10: 'abc'

For now, just be aware this can happen. You will learn how to handle errors gracefully in a later module when we cover try/except.

Tip: When testing your programs, always enter the type of data the program expects. Make sure your prompts clearly tell the user what to enter (e.g., "Enter a number:" not just "Enter:").

Check Your Understanding

Question 1: What type does input() always return?

Answer: String (str). Always. Even if the user types a number.

Question 2: How do you get a decimal number from the user?

Answer: number = float(input("Enter a number: ")) -- wrap input() with float().

Try It Yourself!

  1. Write a program that asks for the user's name and age, then tells them what year they were born (approximately).
  2. Create a program that asks for the length and width of a room, then calculates and prints the area.
  3. Build a "Mad Libs" program that asks for a noun, adjective, and verb, then prints a silly sentence using them.

Key Takeaways

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