Interacting with users through input and output is fundamental to most programs.

name = input("Enter your name: ")
print(f"Hello, {name}!")

⚠️ input() always returns a string! Convert to the required type.

age = int(input("Enter your age: "))
price = float(input("Enter price: $"))

x, y = map(int, input("Enter two numbers: ").split())
print(f"Sum: {x + y}")

while True:
    try:
        age = int(input("Enter your age: "))
        if age < 0 or age > 150:
            print("Enter a realistic age.")
            continue
        break
    except ValueError:
        print("Invalid input! Enter a number.")

# Comma-separated
print("Name:", name, "Age:", age)

# f-strings (preferred)
print(f"Name: {name}, Age: {age}")

# .format()
print("Name: {}, Age: {}".format(name, age))

In real applications, you’ll use:

• Command-line arguments (argparse, sys.argv)
• Environment variables (os.environ)
• Configuration files (.env, .yaml, .json)
• Web forms / API requests

Proper input handling prevents crashes and security vulnerabilities. Always validate user input!

• Forgetting input() returns a string
• Not validating user input
• Using input() in production code (use proper argument parsing instead)

Q1: What does input() return in Python?

A: Always a string. You must convert to the required type using int(), float(), etc.

Q2: How do you get multiple inputs on one line?

A: Use split() with map(): a, b = map(int, input().split())

1. Write a program that asks for name, age, and favorite color, then prints a summary.
2. Create a simple calculator that takes two numbers and an operator.
3. Add input validation for a number guessing game.