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210 CHAPTER 10 ■ BATTERIES INCLUDED
Naming Your Module
As you may have noticed, the file that contains the code of a module must be given the same
name as the module—with an additional .py file name extension. In Windows, you can use the
file name extension .pyw instead. You learn more about what that file name extension means
in Chapter 12.
Packages
To structure your modules, you can group them into packages. A package is basically just another
type of module. The interesting thing about them is that they can contain other modules. While
a module is stored in a file (with the file name extension .py), a package is a directory. To make
Python treat it as a package, it must contain a file (module) named __init__.py. The contents
of this file will be the contents of the package, if you import it as if it were a plain module. For
example, if you have a package named constants, and the file constants/__init__.py contains
the statement PI = 3.14, you would be able to do the following:
import constants
print constants.PI
To put modules inside a package, simply put the module files inside the package directory.
For example, if you wanted a package called drawing, which contained one module called
shapes and one called colors, you would need the files and directories (UNIX pathnames)
shown in Table 10-1.
Table 10-1. A Simple Package Layout
File/Directory
~/python/
~/python/drawing/
~/python/drawing/__init__.py
~/python/drawing/colors.py
~/python/drawing/shapes.py
Description
Directory in PYTHONPATH
Package directory (drawing package)
Package code (“drawing module”)
colors module
shapes module
In Table 10-1, it is assumed that you have placed the directory ~/python in your PYTHONPATH. In
Windows, simply replace ~/python with c:\python and reverse the direction of the slashes (to
backslashes).
With this setup, the following statements are all legal:
import drawing
# (1) Imports the drawing package
import drawing.colors # (2) Imports the colors module
from drawing import shapes # (3) Imports the shapes module