This chapter presents the Python module—the highest-level program organization unit, which packages program code and data for reuse. In concrete terms, modules take the form of Python program files (and C extensions); clients import modules to use the names they define. Modules are processed with two new statements and one important built-in function we explore here:
Lets a client fetch a module as a whole
Allows clients to fetch particular names from a module
Provides a way to reload a module’s code without stopping Python
We introduced module basics in Chapter 1, and you may have been using module files in the exercises, so some of this chapter may be a review. But we also flesh out module details we’ve omitted so far: reloads, module compilation semantics, and so on. Because modules and classes are really just glorified namespaces, we explore namespace basics here as well, so be sure to read most of this chapter before tackling the next.
Let’s start with the obvious first question: why should we care about modules? The short answer is that they provide an easy way to organize components into a system. But from an abstract perspective, modules have at least three roles: