Teach Your Kids To Code: A Parent-friendly Guide to Python Programming

154 Chapter 7

To convert a length in inches to its equivalent in centimeters,

we multiply the number of inches by 2.54—the approximate num-

ber of centimeters in an inch. To pass that calculation back to the

rest of the program, we would use a return statement. The value

after the keyword return will be passed back to the program as the

function’s return value, or result. Let’s define our function:

def convert_in2cm(inches):

return inches * 2.54

If you type these two lines into the Python shell and then type

convert_in2cm(72) and press enter, Python will respond with 182.88.

There are about 182.88 centimeters in 72 inches (or 6 feet—my

height). The value 182.88 is returned by the function, and in the

command line shell, we see the return value printed on the next

line after we call a function.

We could also perform

another useful conversion:

pounds to kilograms. To con-

vert pounds to kilograms, we

divide the weight in pounds

by 2.2, the approximate num-

ber of pounds in 1 kilogram.

Let’s create a function called

convert_lb2kg() that will take a

value in pounds as its param-

eter and return the converted

value in kilograms:

def convert_lb2kg(pounds):

return pounds / 2.2

The return statement is sort of like using parameters in

reverse, except that we can return only one value, not a set of

values like the parameters we take in. (That one value can be a

list, however, so with some work you can pass multiple values back

in a single return variable.)

Using Return Values in a Program

Using these two conversion functions, let’s build a silly application:

a Ping-Pong-ball height and weight calculator. This program will