Lesson 8: What are Functions?

• Allows for code to be reused
• Makes complicated code easier to understand
• Values can be passed to functions as arguments
• Functions can return values

A programmer must define a function before using it on data. In Python, the keyword for defining a new function is def.

Example: The following simple function, HelloWorld(), outputs the string statement “Hello World”:

def HelloWorld():
    print("Hello World")

After a function has been defined, it can be used when the function is called. In Python, you call a function by typing the name of the function. To call the above function, HelloWorld(), use:

HelloWorld()

A function can take either no arguments or one or more arguments.

Example: HelloWorld() has an empty parenthesis because the function has no arguments.

Addition(x,y) requires two arguments, x and y, to be passed in order for the function to return the sum of x and y.

def Addition(x, y):
    return x + y

To find the sum of the numbers 5 and 7 using this Addition() function, a programmer simply passes these values on calling the function:

print('The sum of 5 and 7 is', Addition(5, 7))

A function UserInformation() takes three arguments (name, age, and address) and prints this information as string statements when the function is called:

def UserInformation(name, age, address):
    print("The name of the User is", name)
    print("The age of the user is", age)
    print("The address of the user is", address) 

UserInformation('Patrick', 28, 'Raheen')