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Chapter 21. Modules: The Big Picture

This chapter begins our in-depth 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 extensions coded in external languages such as C, Java, or C#). Each file is a module, and modules import other modules to use the names they define. Modules are processed with two statements and one important function:

import

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

from

Allows clients to fetch particular names from a module

imp.reload

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

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

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

Why Use Modules?

In short, modules provide an easy way to organize components into a system by serving as self-contained packages of variables known as namespaces. All ...

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