In this chapter, we are finally going to write some code! The code in this chapter and all the chapters that follow is written for Python 3.5 (the current release at the time of writing). When modules, syntaxes, or language constructs are not available in earlier versions of Python (for example, Python 2.7), these will be pointed out in this chapter. In general, however, the code presented here should work on Python 2.x with some minor modifications.

Let's go back to some of the ideas presented in the previous chapter. We know that we can structure our algorithms and programs so that they can run on a local machine or on one or more computers across a network. Even when our code runs on a single machine, as we saw, we can use multiple threads and/or multiple processes so that its various parts can run at the same time on multiple CPUs.

We will now pause thinking about multiple CPUs and instead look at a single thread/process of execution. There is a programming...