Function Review

Functions are tricky! It takes a minute to get used to them, but after that they'll be second nature to you. You might find yourself slowing down a bit in this chapter, and if you do, that's totally normal.

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Let's break down this function line by line so you can understand every nook and cranny of it.

def area_of_circle(r):
    pi = 3.14
    result = pi * r * r
    return result

radius = 5
area = area_of_circle(radius)
print(area)
# 78.5

Here's a chronological explanation of what happens when the above code is executed:

def area_of_circle(r):

The area_of_circle function is defined for later use, but not called. It accepts a single input, the arbitrarily named r. The body of the function (pi = 3.14... etc) is ignored for now.

radius = 5

A new variable called radius is created and set to the value 5.

area_of_circle(radius)

The area_of_circle function is called with radius (in this case 5) as the input. Finally, we jump back to the function definition.

def area_of_circle(r):

We will now start executing the body of the function, and r is set to 5.

pi = 3.14

A new variable called pi is created with a value of 3.14.

result = pi * r * r

Some simple math is evaluated (3.14 * 5 * 5) and stored in the result variable.

return result

The result variable is returned from the function as output.

area = area_of_circle(radius)

The returned value is stored in a new variable called area (in this case 78.5).

print(area)

The value of area is printed to the console.