Learning Python

A First Look at Module Files

Earlier in this chapter, we saw how to run module files (i.e., text files containing Python statements) from the operating-system shell’s command line. It turns out that we can also run module files from Python’s interactive command line by importing or reloading them, as we’d normally do from other system components. The details of this process are covered in Chapter 5, but since this turns out to be a convenient way to save and run examples, we’ll give a quick introduction to the process.

The basic idea behind importing modules is that importers may gain access to names assigned at the top level of a module file. The names are usually assigned to services exported by the modules. For instance, suppose we use our favorite text editor to create the one-line Python module file myfile.py, shown in the following code snippet. This may be one of the world’s simplest Python modules, but it’s enough to illustrate basic module use:

title = "The Meaning of Life"

Notice that the filename has a .py suffix: this naming convention is required for files imported from other components. Now we can access this module’s variable title in other components two different ways, either by importing the module as a whole with an import statement and qualifying the module by the variable name we want to access:

% python                        
               Start Python

>>> import myfile               
               Run file, load module as a whole

>>> print myfile.title          
               Use its names: '.' qualification

The Meaning of Life

or by fetching (really, ...