Using **functions** in Python is highly beneficial as they allow you to call the same block of code multiple times without rewriting it, saving time and reducing errors. Moreover, they help break down complex tasks into smaller, manageable steps, with each **function** performing a specific action, making the code more **readable** and easier to maintain.

In simpler terms, __functions__ are like breaking down tasks into smaller pieces that you can use repeatedly. This approach makes your program more __convenient__ to write, change, and understand.

## Defining a Function

Let's define the simplest function in Python.

1. First, use the `def` keyword;
2. Next, specify the **function name** - a unique identifier that represents the function. It follows variables' naming conventions, such as using lowercase letters and underscores (this convention is called **snake_case**);
3. Use `():` after the function name - in these brackets, specify the function's **arguments (parameters)**;
4. Then, specify the **function body** with the indented new line;
5. After the function body, specify the **return value** of the function using different keywords such as `return`, `assign`, or `yield`;
6. Finally, use functions in code. To do so, **call** the function using its name and specifying its parameters.

Let's look at an example. We will create a simple function to print `'Hello, world!'` in the console and use this function in code by calling it.

# Specify the function name
# The function doesn't require any parameters, so we simply use `():`
def print_hello():
    # Function body: we have to use indentation when defining it.
    print('Hello, world!')
    # The function doesn't return anything, so we don't need to write additional code

# Call the function
print_hello()

You may have noticed that we used the `print()` function as the body of `print_hello()`. It is a __built-in function__ that prints text to the console. It takes a string as an argument, which we specify in the `()` brackets.

You might wonder **why this function has no return value if it prints the message in the console**.    
In Python, a function can perform a task (in this case, printing a message) without necessarily returning a value. The presence or absence of a `return` statement in a function depends on whether the function is intended to produce an output (return a value) that can be used in **other parts of the program**.    

The `print_hello()` function prints a string to the console, but we can't use this string in the program, manipulate it, or use it as input for other functions. Therefore, the `print_hello()` function has no return value.

You'll have a solid grasp of how important functions are in Python, no matter your field in computer science. We'll cover creating functions, defining arguments, handling return values, and exploring their use in Python.

We will consider what a function in Python and some basic techniques used to create functions is: what are the arguments of the function, what is the return value of the function, what is the body of the function, and how to use the function in the code.

Learn how to define functions in Python using positional and optional arguments. Master the flexibility of creating functions that adapt to different input scenarios.

Learn to work with arbitrary arguments and keyword arguments in Python to handle variable numbers of inputs. Understand how arbitrary arguments manage flexible positional inputs and how keyword arguments organize named arguments into a dictionary for efficient function design.

The return value of a function is the direct result of the execution of the function, which we can use in the program. There are several types of function return values - we will consider the most commonly used.

Explore the power of recursion and lambda functions in Python. Understand how recursion allows a function to call itself for solving complex problems, and how lambda functions provide a concise way to define anonymous functions for simple tasks.

Python Functions Tutorial

What Is Function?

Defining a Function