As we noted in the previous chapters, we'll often use Python's for loop to work with collections. When working with materialized collections such as tuples, lists, maps, and sets, the for loop involves an explicit management of state. While this strays from purely functional programming, it reflects a necessary optimization for Python. If we assure that state management is localized to an iterator object that's created as part of the for statement evaluation, we can leverage this feature without straying too far from pure, functional programming. For example, if we use the for loop variable outside the indented body of loop, we've strayed too far from purely functional programming.

We'll return to this in Chapter 6, Recursion and Reduction. It's an important topic, and we'll just scratch the surface here with a quick example of working with generators.

One common application of for loop iterable processing is the unwrap(process(wrap(iterable))) design pattern. A wrap...