Course Content

Python Functions Tutorial

1. What is Function in Python?

What Is Function?Challenge: Building functions Arguments Return Value Function Body Built-in Functions

2. Positional and Optional Arguments

Positional Arguments Challenge: Positional Arguments Optional Arguments Challenge: Optional Arguments

3. Arbitrary Arguments

Arbitrary Arguments Arbitrary Keyword Arguments Combination of Positional and Optional Arguments

4. Function Return Value Specification

Single Return Value Multiple Return Values None Return Value Generator Functions Challenge: Traffic lights

5. Recursion and Lambda Functions

Recursion Challenge: Pyramid Lambda Functions Immediately Invoked Lambda Expression Writing Effective and Maintainable Functions

What Is Function?

In Python, a function is a named block of reusable code that performs a specific task. It is a fundamental concept in programming and plays a crucial role in organizing and structuring code. Functions are like building blocks in LEGO. They allow you to create reusable chunks of code that can be used in different parts of your program.

Firstly, it's convenient because you can call the same block of code multiple times without having to rewrite it. This saves time and reduces the chance of making mistakes;
Secondly, functions help break down complex tasks into smaller, understandable steps. Each function can perform a specific action, making the code more readable and easier to manage.

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

Defining a function

Let's to define the most simple function in Python.

Firstly, the def keyword has to be used;
Secondly, we have to 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);
We have to use (): after the function name - in these brackets, we specify the function's arguments (parameters);
Then, we specify the function body with the indented new line;
After the function body, we can specify the return value of the function using different keywords such as return, assign, or yield;
Finally, we can use functions in code. To do so, we have to call function using its name and specifying its parameters.

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


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# Specify function name. Function does't require any paramters so we simply use ():
def print_hello():
# Function body. We have to use indentation when specifying it.
	print('Hello, world!')
# Function does't return anything so we don't need to write some additional code

# Call the function
print_hello()

You may ask 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 in the console, but we can't use this string in the program, manipulate it, or use it as an input for other functions. So, the print_hello() function has no return value.

In the next chapter, you will create your first function.

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Section 1. Chapter 1