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Python Functions

Welcome to your Python Functions crash course! This lesson will walk you through the basics of creating and using functions in Python. Simple language, simple code, powerful skills.

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📌 What Is a Function?

A function is a block of code that only runs when it's called. You can pass data into a function, and it can return data as a result.

✅ Why Use Functions?

• Keeps your code organized
• Avoids repetition (DRY principle: Don't Repeat Yourself)
• Makes code easier to read and debug
• Helps with reusability in larger programs

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🧠 Learning Goals

By the end of this, you’ll be able to:

1. Write your own functions
2. Use arguments and return values
3. Understand function scope
4. Use default, variable, and keyword arguments
5. Work with small extras like lambda and decorators

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🧩 Table of Contents

1. Basic Function
2. Arguments
3. Return Values
4. Default Arguments
5. *args and **kwargs
6. Lambda Functions
7. Function Scope
8. Decorators (Intro)
9. Practice Exercises
10. More Learning Links

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1. 📌 Basic Function

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

greet()

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2. 🧾 Arguments

def greet_user(name):
    print("Hello, " + name)

greet_user("Sarah")

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3. 🔁 Return Values

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

result = add(5, 3)
print(result)

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4. ⚙️ Default Arguments

def greet(name="friend"):
    print("Hello, " + name)

greet()
greet("Lerato")

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5. 📦 *args and **kwargs

def total(*numbers):
    print(sum(numbers))

total(2, 4, 6)

def print_info(**info):
    print(info)

print_info(name="Alex", age=30)

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6. ⚡ Lambda Functions

square = lambda x: x * x
print(square(4))

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7. 🔒 Function Scope

def show():
    message = "Hello inside"
    print(message)

show()
# print(message)  # This will give an error – variable not available outside the function

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8. 🎁 Decorators (Intro)

def decorator(func):
    def wrapper():
        print("Before the function runs")
        func()
        print("After the function runs")
    return wrapper

@decorator
def say_hi():
    print("Hi!")

say_hi()

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9. 📝 Practice Exercises

Try writing these on your own:

• A function to multiply two numbers
• A function that returns "Even" or "Odd" based on a number
• A function that greets a list of names
• A function that calculates the factorial of a number using recursion
• A lambda function that adds 10 to a given number

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10. 🔗 More Learning Links

• Python Docs – Functions
• W3Schools – Python Functions
• Real Python – Functions Guide
• Programiz – Python Functions
• GeeksForGeeks – Python Functions

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💬 Final Thought

Functions are your first real tool to write smarter Python. Master them early, and everything else becomes easier.

Happy coding! 🚀

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