Page 57 - Programming the Raspberry Pi Getting Started with Python

5

Modules, Classes, and Methods

In this chapter, we discuss how to make and use our own modules, like the random module we used in
Chapter 3. We also discuss how Python implements object orientation, which allows programs to be
structured into classes, each responsible for its own behavior. This helps to keep a check on the
complexity of our programs and generally makes them easier to manage. The main mechanisms for
doing this are classes and methods. You have already used built-in classes and methods in earlier
chapters without necessarily knowing it.
Modules
Most computer languages have a concept like modules that allows you to create a group of functions
that are in a convenient form for others to use—or even for yourself to use on different projects.

Python does this grouping of functions in a very simple and elegant way. Essentially, any file with
Python code in it can be thought of as a module with the same name as the file. However, before we
get into writing our own modules, let’s look at how we use the modules already installed with Python.
Using Modules
When we used the random module previously, we did something like this:

The first thing we do here is tell Python that we want to use the random module by using the import

command. Somewhere in the Python installation is a file called random.py that contains a randint
function as well as some other functions.
With so many modules available to us, there is a real danger that different modules might have
functions with the same name. In such a case, how would Python know which one to use? Fortunately,
we do not have to worry about this happening because we have imported the module, and none of the

functions in the module are visible unless we prepend the module name and then a dot onto the front
of the function name. Try omitting the module name, like this:

Having to put the module name in front of every call to a function that’s used a lot can get tedious.
Fortunately, we can make this a little easier by adding to the import command as follows:

This gives the module a local name within our program of just r rather than random, which saves us
a bit of typing.
If you are certain a function you want to use from a library is not going to conflict with anything in
your program, you can take things a stage further, as follows:

To go even further, you can import everything from the module in one fell swoop. Unless you know
exactly what is in the module, however, this is not normally a good idea, but you can do it. Here’s
how: