User Input and Output

Interacting with users is a fundamental part of many Python programs. Python provides simple functions to read input from users and output information to the screen.

Output: print()

The print() function is used to display messages, variables, or results on the screen.

Basic Usage:

# Print a string
print("Hello, World!")

# Print variables
name = "Alice"
age = 30
print("Name:", name, "Age:", age)

# Using f-strings for output
print(f"My name is {name} and I am {age} years old.")

Printing with Formatting

You can customize the output format:

# Print with separators
print("Python", "is", "fun", sep=" - ")  # Python - is - fun

# Print with an end character
print("This is line 1.", end=" ")
print("This is line 2.")  # This is line 1. This is line 2.

Input: input()

The input() function allows you to read input from the user. It always returns the input as a string.

Basic Usage:

# Reading input
name = input("What is your name? ")
print(f"Hello, {name}!")

Converting Input

Since input() returns a string, you may need to convert it to other types like integers or floats.

# Converting to an integer
age = input("Enter your age: ")
age = int(age)
print(f"You are {age} years old.")

# Converting to a float
height = float(input("Enter your height in meters: "))
print(f"Your height is {height}m.")

Handling Multiple Inputs

You can split user input into multiple values using the split() method:

# Input multiple values
data = input("Enter two numbers separated by space: ")
a, b = map(int, data.split())
print(f"Sum: {a + b}")

Common Use Cases

Greeting Example:

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

Adding Numbers:

num1 = int(input("Enter the first number: "))
num2 = int(input("Enter the second number: "))
print(f"The sum is: {num1 + num2}")

Custom Output Formatting:

item = input("Enter an item: ")
price = float(input("Enter the price: "))
print(f"The price of {item} is ${price:.2f}.")

Practice Exercises

1. Write a program to:
   • Ask the user for their first and last name.
   • Print a greeting that includes their full name.
2. Write a program to:
   • Ask the user for two numbers.
   • Calculate and display their sum, difference, product, and quotient.
3. Create a program that:
   • Asks the user for their birth year.
   • Calculates and displays their current age (use 2025 as the current year).
4. Ask the user for three numbers separated by spaces. Calculate and print:
   • Their sum.
   • Their average.

Mastering user input and output is essential for creating interactive Python programs!