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5.1 Why Use Modules?

Let's start with the obvious first question: why should we care about modules? The short answer is that they provide an easy way to organize components into a system. But from an abstract perspective, modules have at least three roles:

Code reuse

As we saw in Chapter 1, modules let us save code in files permanently.[1] Unlike code you type at the Python interactive prompt (which goes away when you exit Python), code in module files is persistent梚t can be reloaded and rerun as many times as needed. More to the point, modules are a place to define names (called attributes) that may be referenced by external clients.

[1] Until you delete the module file, at least.

System namespace partitioning

Modules are also the highest-level program organization unit in Python. As we'll see, everything "lives" in a module; code you execute and some objects you create are always implicitly enclosed by a module. Because of that, modules are a natural tool for grouping system components.

Implementing shared services or data

From a functional perspective, modules also come in handy for implementing components shared across a system, and hence only require a single copy. For instance, if you need to provide a global data structure that's used by more than one function, you can code it in a module that's imported by many clients.

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