Python Functions

Functions are fundamental building blocks in Python, enabling you to write reusable and organized code. In this tutorial, you’ll learn how to define, call, and effectively use functions.

What is a Function?

In Python, a function is a reusable block of code designed to perform a specific task. Functions allow you to break down your code into smaller, manageable chunks, improving readability, maintainability, and modularity.

Here’s an analogy:

• Function: A recipe for baking a cake
• Input: Ingredients (parameters/arguments)
• Output: Finished cake (returned value)

Defining a Function

To define a function in Python, use the def keyword, followed by the function name and parentheses (). End the declaration line with a colon :.

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

Calling a Function

To call (invoke) a function, simply use the function’s name followed by parentheses:

# Calling the greet function
greet()

Output:

Hello, World!

Function Parameters and Arguments

Functions can take parameters (inputs) that allow them to perform different tasks based on different values.

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

# Calling with argument
greet("Alice")

Output:

Hello, Alice!

Returning Values

Functions can also return values using the return keyword, allowing you to reuse the result elsewhere:

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

result = add(10, 5)
print(result)

Output:

15

Default Parameter Values

You can assign default values to function parameters. If an argument isn’t provided, Python will use the default value:

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

greet("Alice")
greet()

Output:

Hello, Alice!
Hello, Guest!

Variable-Length Arguments

Sometimes, you don’t know how many arguments a function might receive. Python allows you to handle this using:

• *args: For non-keyword variable-length arguments
• **kwargs: For keyword variable-length arguments

Example with *args:

def print_numbers(*args):
    for num in args:
        print(num)

print_numbers(1, 2, 3, 4)

Output:

1
2
3
4

Example with **kwargs:

def user_info(**kwargs):
    for key, value in kwargs.items():
        print(f"{key}: {value}")

user_info(name="Alice", age=30)

Output:

name: Alice
age: 30

Keyword Arguments

You can specify arguments by name rather than position. This increases readability:

def describe_pet(name, animal):
    print(f"I have a {animal} named {name}.")

describe_pet(animal="dog", name="Buddy")

Output:

I have a dog named Buddy.

Example with Docstrings:

def multiply(a, b):
    """Multiply two numbers and return the result."""
    return a * b

print(multiply(3, 4))