Code Reuse & Modularity (aka a quick detour into modules, packages, and libraries)

Code Reuse & Modularity (aka a quick detour into modules, packages, and libraries)#

As we move forward in Python, we’re going to be encountering the terms package, module, and library. All of these terms refer to external Python programs that we can use in our program without having to recreate the entire original code. We can think of these resources as “expansion packs” for Python that expand or extend the programming language’s built-in functionality.

A few preliminary definitions…

A module is a Python file that typically includes specialized functions and variables. Modules typically have .py file extensions.
A single or simple directory of modules is called a package. Packages are typically a simple directory with multiple modules.
A library includes blocks of code that can be reused within a program. Libraries are a collection of modules that have a much more complex directory/sub-directory/etc structure than packages

Some modules, packages, and libraries are built-in to Python and require no additional installation. Others have to be installed (typically at the command line, or in the terminal) before you can import and use them in a program.

Built-In Functions#

Built-in functions don’t require any extra steps to be able to access them in the programming environment. For example, you can see the source code for the print() function, contained in bltinmodule.c file in Python’s source code. But all we have to do is use the function name in our program.

Modules & Packages#

In this example, we have a game package that includes sound, image, and level sub-packages. Each of those sub-packages includes specific modules. For example, the sound sub-package includes the load.py, play.py, and pause.py modules.

We can bring these modules into our program using an import statement.

For example, let’s say we wanted to bring the start.py module from the level sub-package into our program.

We could do this using the following import statement at the start of our program.

from game.level import start

Now, we would be able to access any of the functions (or other code) contained in the start.py module, because we have imported them into our program.