2.5 Input and Output in Python

Introduction

Python provides built-in functions for handling input (getting data from users) and output (displaying data on the screen). These functions allow interaction between the user and the program.

This section covers:

• How to use the input() function to get user input
• How to use the print() function to display output
• Formatting output for better readability

By the end of this lesson, you will be able to create interactive Python programs that accept input from users and display formatted output.

2.5.1 Taking User Input with input()

The input() function allows a program to receive user input as a string.

Basic Usage of input()

name = input("Enter your name: ")
print("Hello,", name)

How It Works:

1. The input() function displays the prompt ("Enter your name: ").
2. The user enters a value and presses Enter.
3. The entered value is stored in the variable name as a string.
4. The print() function displays a greeting using the input value.

Example Output:

Enter your name: Alice
Hello, Alice

2.5.2 Handling Numeric Input

By default, input() returns a string. If you need a number, convert the input using int() or float().

Converting Input to an Integer

age = input("Enter your age: ")
age = int(age)  # Convert string to integer
print("Next year, you will be", age + 1)

Example Output:

Enter your age: 25
Next year, you will be 26

Converting Input to a Float

height = float(input("Enter your height in meters: "))
print("Your height is", height, "meters.")

Example Output:

Enter your height in meters: 1.75
Your height is 1.75 meters.

If the user enters non-numeric characters, Python will raise a ValueError. To prevent this, always validate input before conversion.

2.5.3 Displaying Output with print()

The print() function is used to display output. It can print strings, numbers, and variables.

Printing Multiple Values

You can print multiple values by separating them with commas (,).

name = "Alice"
age = 25
print("Name:", name, "Age:", age)

Example Output:

Name: Alice Age: 25

Python automatically adds a space between values when using commas.

2.5.4 Formatting Output

1. Using sep to Customize Separators

By default, print() separates values with a space. You can change this using sep.

print("Python", "is", "awesome", sep="-")

Example Output:

Python-is-awesome

2. Using end to Control Line Endings

By default, print() adds a newline (\n) at the end. You can change this using end.

print("Hello", end=" ")
print("World!")

Example Output:

Hello World!

3. Using f-strings for Formatted Output

F-strings (f"") allow inserting variables directly into strings.

name = "Alice"
age = 25
print(f"My name is {name} and I am {age} years old.")

Example Output:

My name is Alice and I am 25 years old.

4. Using .format() for Formatted Output

The .format() method is an alternative to f-strings.

name = "Alice"
age = 25
print("My name is {} and I am {} years old.".format(name, age))

Example Output:

My name is Alice and I am 25 years old.

2.5.5 Taking Multiple Inputs

You can take multiple inputs in a single line using .split().

name, age = input("Enter your name and age: ").split()
print(f"Name: {name}, Age: {age}")

Example Output:

Enter your name and age: Alice 25
Name: Alice, Age: 25

Here, .split() separates input values based on spaces.

If you need a comma-separated input, specify "," in .split():

name, age = input("Enter your name and age separated by a comma: ").split(",")
print(f"Name: {name}, Age: {age}")

2.5.6 Summary

Here is a summary of what we have covered in this section

• input() is used to get user input. By default, it returns a string.
• Convert input using int(), float() when working with numbers.
• print() displays output and supports multiple values.
• Use sep and end to customize print behavior.
• Use f-strings (f"") or .format() for formatted output.
• .split() allows multiple inputs on a single line.

What’s Next?

In the next exercise, you will apply what you have learned by writing a Python program that takes user input and displays formatted output.