📥 Python Input and Output (I/O): A Complete Guide

What is Input/Output in Python?

Input/Output (I/O) is how a program communicates with the outside world. In Python, input refers to data that comes from the user (via keyboard, files, or other sources), while output refers to data that the program sends out (to the console, files, or other destinations).

Think of a program like a conversation. The program asks questions (output), you respond (input), and the program processes your response and responds back (output). This interaction is the foundation of interactive programming.

# Simple Input/Output Example
name = input("What's your name? ")  # Input
print("Hello, " + name + "!")       # Output

1. The input() Function

The input() function is used to accept user input from the keyboard. It reads a line of text from the user and returns it as a string.

# Basic input() usage
name = input("What is your name? ")
print("Nice to meet you, " + name + "!")

# Output:
# What is your name? (user types: Alice)
# Nice to meet you, Alice!

2. Type Conversion with input()

Since input() always returns a string, you need to convert it to the desired data type for numerical operations.

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

# Converting input to float
price = float(input("Enter the price: "))
print("Price with 10% tax:", price * 1.10)

# Output:
# Enter your age: 25
# Next year you will be 26
# Enter the price: 50.50
# Price with 10% tax: 55.55

# Multiple inputs in one line
x, y = input("Enter two numbers: ").split()
x = int(x)
y = int(y)
print("Sum:", x + y)

# Output:
# Enter two numbers: 10 20
# Sum: 30

3. The print() Function

The print() function is used to display output to the console. It can accept multiple arguments and automatically adds a space between them.

# Basic print() usage
print("Hello, World!")

# Print with multiple arguments
print("The answer is", 42)

# Print with variables
name = "Python"
version = 3.12
print("Language:", name, "Version:", version)

# Output:
# Hello, World!
# The answer is 42
# Language: Python Version: 3.12

4. Print Formatting

Python provides several ways to format output. Let's explore the most common and modern approaches.

a. f-strings (Formatted String Literals)

f-strings are the most modern and recommended way to format strings in Python. They are introduced in Python 3.6 and are both readable and efficient.

# f-string examples
name = "Python"
version = 3.12
year = 2024

print(f"Language: {name}, Version: {version}, Year: {year}")

# With expressions
radius = 5
print(f"Area of circle: {3.14 * radius * radius:.2f}")

# Output:
# Language: Python, Version: 3.12, Year: 2024
# Area of circle: 78.50

b. The format() Method

The format() method is another way to format strings. It uses placeholders {} in the string and passes values to them.

# format() examples
name = "Python"
version = 3.12

print("Language: {}, Version: {}".format(name, version))

# Positional formatting
print("Name: {0}, Age: {1}".format("Alice", 25))

# Named formatting
print("Name: {name}, Age: {age}".format(name="Bob", age=30))

# Output:
# Language: Python, Version: 3.12
# Name: Alice, Age: 25
# Name: Bob, Age: 30

5. Escape Sequences

Escape sequences are special characters used to control how text is displayed. They begin with a backslash \.

# Escape sequence examples
print("Line 1\nLine 2")
print("Column 1\tColumn 2")
print("She said, \"Hello!\"")
print("Path: C:\\Users\\Documents")

# Output:
# Line 1
# Line 2
# Column 1    Column 2
# She said, "Hello!"
# Path: C:\Users\Documents

6. File Input/Output

Python can read from and write to files using the open() function. This allows you to store data permanently.

# Writing to a file
with open("example.txt", "w") as file:
    file.write("Hello, Python!\n")
    file.write("This is a second line.")

# Reading from a file
with open("example.txt", "r") as file:
    content = file.read()
    print(content)

# Output:
# Hello, Python!
# This is a second line.

# Reading line by line
with open("example.txt", "r") as file:
    for line in file:
        print(line.strip())

# Output:
# Hello, Python!
# This is a second line.

Try It Yourself!

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Frequently Asked Questions

📚 Where to Go From Here

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