Intro to Functions

Functions are an important building block for writing programs. They are like smaller bite-sized programs within your main program that can be executed to perform operations for you. They are great for compartmentalizng your code and breaking it down into smaller parts that are easier to read and test.

Functions usually receive some data as an input and return a result as output. If you have to repeat a calculation in your program, it's good practice to put it inside a function so you don't have to have redundant code in your program.

Let's get started.

Functions have two parts- function definitions and function calls.

Functions definitions look like this:

# Function Definition
def my_function(parameter1, parameter2):
  # do something
  return result

def tells python that you are defining a function. Then you give it a name (my_function in this example).

In parentheses, you see two parameters. You can have as many or as few parameters as you want. Note that order matters (has to match the order of the function call). These are parameters the function receives as input to process. Note the keyword return in the function definition. That means this function is going to have an output. When we get to the function call, we can see what happens to the output.

The function call is going to look similar to the function definition.

# Function Call
# This is a function call, where we tell python to run our function. 
# It's storing the function output that is returned in a new variable called function_result
function_result = my_function(argument1, argument2)

# Or you can give literal arguments and just send numbers instead of variables
function_result = my_function(1, "bob")

You use the functions name, and pass it arguments (function inputs). They are called arguments in a function call and parameters in a function definition. Note the difference.

These arguments are sent to the function definition and are saved using the parameter names. When we run the first function call below, argument1 is stored in a variable called parameter1 and argument2 is stored in a variable called parameter2 in the function definition when it runs.

Then the code executes and we see the return statement in the function definition telling python our function has output. That output can be stored in a new variable when we call the function. We store it in a variable called function_result.

Once you have a function defined, you can call it as many times as you want. You can put function calls inside other functions. The sky is the limit!

Those are the basics.

Functions are generally used if some code is repeated or to break code down into smaller chunks that are easier to handle. Good luck!

Read up on functions in more detail in the following readings.

Reading material

Optional Readings:
Intro from the living pearl
 Syntax, return, and param sections of Python Course