Learning Python, 2nd Edition

Chapter 15. Modules: The Big Picture

This chapter begins our look at the Python module, the highest-level program organization unit, which packages program code and data for reuse. In concrete terms, modules usually correspond to Python program files (or C extensions). Each file is a module, and modules import other modules to use the names they define. Modules are processed with two new statements and one important built-in function:

import

Lets a client (importer) fetch a module as a whole

from

Allows clients to fetch particular names from a module

reload

Provides a way to reload a module’s code without stopping Python

We introduced module fundamentals in Chapter 3, and have been using them ever since. Part V begins by expanding on core module concepts, and then moves on to explore more advanced module usage. This first chapter begins with a general look at the role of modules in overall program structure. In the next and following chapters, we’ll dig into the coding details behind the theory.

Along the way, we’ll flesh out module details we’ve omitted so far: reloads, the __name__ and __all__ attributes, package imports, and so on. Because modules and classes are really just glorified namespaces, we formalize namespace concepts here as well.

Why Use Modules?

Modules provide an easy way to organize components into a system, by serving as packages of names. From an abstract perspective, modules have at least three roles:

Code reuse

As we saw in Chapter 3, modules let us save code ...