num1 = 5

num2 = 3

sum = num1 + num2

print(sum)

Above we have a simple adding number program. It's basic and it has to be manually changed and updated if we wish to add different numbers together. So we will use that as an example to convert it into a function. This is an example of D.R.Y. principles. Don't repeat yourself. We ideally write our code to be modular and reusable. It is also much faster when python is running to have code written in functions. We will get into that after we learn how to write functions.

def add_numbers(num1, num2):

sum = num1 + num2

return sum

print(add_numbers(5, 3)

Above is the basics of a function. We start with def then give our function a name. Here we use add_numbers as the name of the function followed by parentheses and a colon. Inside the parentheses we define the arguments of the function. This is the important part: this is what allows the function to be reusable in the same way over and over. Since we are making an adding function for 2 numbers, we can use our variables num1 and num2. Then we use the same line of code we had before: sum = num1 + num2. That's the logic of the function. Then we add a return statement to finish it and we put the result of our function. Which is sum in this function. If you run that code you will not get any errors, but nothing will happen either. When you define a function you basically establish the recipe for the code. You have to call the function to cook the recipe. To call it you use the function name add_numbers(). You then have to pass the arguments in the function. This can be any number, then a comma, and another number. I highlighted the different variables in the function to show you how they are used throughout the function.

Introduction to functions