Tutorial on Functions

Here’s a beginner-friendly tutorial on Functions in Python 🐍✨—with emojis, step-by-step explanations, practice questions, and solutions!

🚦 What is a Function?

A function is a named block of code that performs a specific task. You can use (call) a function whenever you need that task done—no need to repeat code!

• Built-in functions: Already available in Python (like print(), len(), type())
• User-defined functions: You create these using the def keyword.

📝 Why Use Functions?

• Avoid repetition: Write code once, use it many times!
• Organize code: Break a big problem into smaller, manageable parts.
• Make code reusable: Use your functions in other programs too!

🛠️ How to Define and Call a Function

1️⃣ Defining a Function

def greet():
    print("Hello, world!")

• def starts the function definition.
• greet is the function name.
• () are parentheses (can include parameters).
• : starts the function body (code inside the function).
• Indent the body (usually 4 spaces).

2️⃣ Calling a Function

greet()  # Output: Hello, world!

Just write the function name followed by parentheses!

🎯 Functions with Parameters

Parameters let you pass information to a function.

def greet(name):
    print("Hello,", name)

greet("Alice")  # Output: Hello, Alice
greet("Bob")    # Output: Hello, Bob

Here, name is a parameter. When you call the function, you provide an argument.

🔙 Functions that Return Values

Use return to send a value back to the caller.

def add(a, b):
    return a + b

result = add(3, 5)
print(result)  # Output: 8

The function calculates and returns the sum.

🧠 Local and Global Variables

• Local variable: Defined inside a function; used only there.
• Global variable: Defined outside all functions; can be used anywhere.

def foo():
    x = 10  # local to foo
    print(x)

x = 5  # global
foo()      # Output: 10
print(x)   # Output: 5

💡 Practice Questions

1️⃣ Write a function that prints “Good morning!”

def wish():
    print("Good morning!")

wish()  # Output: Good morning!

2️⃣ Write a function that takes two numbers and prints their product.

def multiply(a, b):
    print(a * b)

multiply(4, 5)  # Output: 20

3️⃣ Write a function that returns the square of a number.

def square(n):
    return n * n

print(square(7))  # Output: 49

4️⃣ Write a function that takes a string and prints it in uppercase.

def shout(text):
    print(text.upper())

shout("hello")  # Output: HELLO

🏗️ Step-by-Step Example: Sum of a List

Problem: Write a function that takes a list of numbers and returns their sum.

Step 1: Define the function with a parameter for the list. Step 2: Initialize a total variable to 0. Step 3: Loop through each number in the list and add it to total. Step 4: Return the total.

def list_sum(numbers):
    total = 0
    for num in numbers:
        total += num
    return total

print(list_sum([1, 2, 3, 4]))  # Output: 10

⭐ Key Points

• Use def to define a function.
• Call a function by its name with parentheses.
• Use parameters to pass data into functions.
• Use return to send data back from a function.
• Functions help you organize and reuse code.

Try making your own functions for daily tasks—practice is the best way to learn! 😃🧑‍💻

References:

• [Think Python, Chapter 3]¹
• [Python-IITM-Foundational-Course.pdf]²