Python Cookbook, 3rd Edition

Chapter 10. Modules and Packages

Modules and packages are the core of any large project, and the Python installation itself. This chapter focuses on common programming techniques involving modules and packages, such as how to organize packages, splitting large modules into multiple files, and creating namespace packages. Recipes that allow you to customize the operation of the import statement itself are also given.

10.1. Making a Hierarchical Package of Modules

Problem

You want to organize your code into a package consisting of a hierarchical collection of modules.

Solution

Making a package structure is simple. Just organize your code as you wish on the file-system and make sure that every directory defines an __init__.py file. For example:

    graphics/
        __init__.py
        primitive/
             __init__.py
             line.py
             fill.py
             text.py
        formats/
             __init__.py
             png.py
             jpg.py

Once you have done this, you should be able to perform various import statements, such as the following:

import graphics.primitive.line
from graphics.primitive import line
import graphics.formats.jpg as jpg

Discussion

Defining a hierarchy of modules is as easy as making a directory structure on the filesystem. The purpose of the __init__.py files is to include optional initialization code that runs as different levels of a package are encountered. For example, if you have the statement import graphics, the file graphics/__init__.py will be imported and form the contents of the graphics namespace. For an import such as import graphics.formats.jpg ...