Welcome back! Yesterday, we learned about control structures in Python. Today, we’ll explore functions, which are essential for organizing and reusing code. By the end of this day, you’ll be able to create and use your own functions to make your programs more modular and efficient. Let’s get started!

What are Functions?
Functions are blocks of code that perform a specific task and can be reused throughout your program. They help make your code more organized, readable, and maintainable.

Defining Functions
You can define a function using the def keyword, followed by the function name and parentheses. Here’s the basic syntax:

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def function_name(parameters):

Code block

return value

Example:

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def greet(name):
print(f"Hello, {name}!")

greet("Andrew")
Parameters and Arguments
Functions can accept parameters, which are values you pass into the function. Parameters allow you to customize the behavior of your functions.

Example:

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

result = add(3, 5)
print(result) # Output: 8
Return Values
Functions can return values using the return statement. This allows you to send the result of a function back to the caller.

Example:

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def square(number):
return number * number

result = square(4)
print(result) # Output: 16
Default Parameters
You can provide default values for parameters, which are used if no argument is passed when the function is called.

Example:

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def greet(name="Guest"):
print(f"Hello, {name}!")

greet() # Output: Hello, Guest!
greet("Andrew") # Output: Hello, Andrew!
Keyword Arguments
When calling a function, you can use keyword arguments to specify which parameter each value should be assigned to.

Example:

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def describe_pet(pet_name, animal_type="dog"):
print(f"I have a {animal_type} named {pet_name}.")

describe_pet(pet_name="Buddy", animal_type="cat") # Output: I have a cat named Buddy.
describe_pet("Charlie") # Output: I have a dog named Charlie.
Practice Time!
Let’s put what we’ve learned into practice. Write a Python program that defines and uses functions with parameters, return values, default parameters, and keyword arguments.

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Function to calculate the area of a rectangle

def calculate_area(length, width):
return length * width

Function to greet a user with a default name

def greet(name="Guest"):
print(f"Hello, {name}!")

Function to describe a pet with keyword arguments

def describe_pet(pet_name, animal_type="dog"):
print(f"I have a {animal_type} named {pet_name}.")

Using the functions

area = calculate_area(5, 3)
print(f"Area: {area}") # Output: Area: 15

greet() # Output: Hello, Guest!
greet("Andrew") # Output: Hello, Andrew!

describe_pet(pet_name="Buddy", animal_type="cat") # Output: I have a cat named Buddy.
describe_pet("Charlie") # Output: I have a dog named Charlie.
Conclusion
Great job today! You’ve learned how to define and use functions in Python, making your code more modular and reusable. Tomorrow, we’ll dive into error handling, which is essential for writing robust programs. Keep practicing and having fun coding!