Cover by Mark Lutz

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Chapter 22. Module Coding Basics

Now that we’ve looked at the larger ideas behind modules, let’s turn to a simple example of modules in action. Python modules are easy to create; they’re just files of Python program code created with a text editor. You don’t need to write special syntax to tell Python you’re making a module; almost any text file will do. Because Python handles all the details of finding and loading modules, modules are also easy to use; clients simply import a module, or specific names a module defines, and use the objects they reference.

Module Creation

To define a module, simply use your text editor to type some Python code into a text file, and save it with a “.py” extension; any such file is automatically considered a Python module. All the names assigned at the top level of the module become its attributes (names associated with the module object) and are exported for clients to use.

For instance, if you type the following def into a file called module1.py and import it, you create a module object with one attribute—the name printer, which happens to be a reference to a function object:

def printer(x):                   # Module attribute
    print(x)

Before we go on, I should say a few more words about module filenames. You can call modules just about anything you like, but module filenames should end in a .py suffix if you plan to import them. The .py is technically optional for top-level files that will be run but not imported, but adding it in all cases makes your files’ types more ...

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