Python Programming for Raspberry Pi, Sams Teach Yourself in 24 Hours

By the Way: Importing Near the Beginning

A good rule of thumb for importing modules—custom or standard—into your Python

script is to do it at the top of the script. Therefore, in Python scripts, put in all your

import statements after the leading documentation lines.

Try It Yourself: Create and Use a Custom Module in Python

In the following steps, you are going to create a custom module. In essence, you will be

following the seven steps just described to create it, test it, and then move it into

production.

Pretend that you have two great functions. One, called discountp, that shows the

actual price of an item if you give it the original price and the listed discount. The

other function, priceper, shows the price per item when the prices at a store are

shown for a group of items (for example, 3 for $11).

You decide to put these two useful functions into their own module so that you can use

them in several scripts. Next, you determine that shopper would be a good module

name. It is a nice, short name, and it is not a Python keyword. Next, you need to put the

two functions into a file called shopper.py. This is where you start in the following

steps:

1. If you have not already done so, power up your Raspberry Pi and log in to the
   system.


2. If you do not have the LXDE GUI started automatically at boot, start it now by typing
   startx and pressing Enter.


3. Open the LXTerminal by double-clicking the LXTerminal icon.


4. At the command-line prompt, type nano py3prog/shopper.py and press
   Enter. The command puts you into the nano text editor and creates the custom module
   shopper.py in the /home/pi/py3prog directory.


5. Type the following code into the nano editor window, pressing Enter at the end of
   each line:

By the Way: Be Careful!

Be sure to take your time here and avoid making typographical errors. You can

make corrections by using the Delete key and the up- and down-arrow keys.

Click here to view code image

def discountp(percentage, price):

return round(price -((percentage /100) * price),2)

def priceper(no_items, price):

return round(price / no_items,2)

6. Double-check to make sure you have entered the code into the nano text editor
   window as shown above. Make any corrections needed.