Functions

You have already used some functions in Python, such as print and input. While they are “in-built” and you can’t see their code, they were created in a very similar way to the programs you have written. In this next section you will create your own functions.

Note: This course has a simple introduction to functions; you can learn more about functions, including how to pass and return variables, in Programming 102: Think Like a Computer Scientist.

You may hear functions referred to as subroutines or procedures. In some other programming languages, subroutines and functions are different things, but in Python they are all just known as functions.

The syntax to create a function in Python looks like this:

def my_function():
 print("do this")

def stands for “definition”, since what you are doing when creating a function is defining it and giving it a name.

Between the def and the () is the name of your function followed by :. Indented under the : is the code which should be run as part of the function.

When you want to use (or call) a function you use the name with parentheses:

my_function()

Tip: Like variables, functions can be given any name you wish, but it is a good idea to name your functions after the job they do.

Let’s explore how to use functions in Python.

• Create a new program called functions.

• Use def to add a function at the top of your program called intro.

def intro():

• Indented under this line, add some code to print a message.

 print("lets do some coding.")

• Call your intro function from your program.

Note: this line of code is not indented under the def as it doesn’t belong to the function definition.

intro()

Your program should now look similar to this:

def intro():
 print("lets do some coding.")
 
intro()

• Run your program. You should see your message.

• Change your code so the function is run twice, by adding a second call to intro at the bottom of your program.

intro()
intro()

• Run your program again. You will see that the message is printed twice.

Using functions in this way allows you to reuse your code: you don’t have to write out all the steps every time. It also makes the code easier to understand and change.

Try amending your intro function so it prints out a second message or asks the user for some input.