Mathematically, a function is a mapping of values in a domain to values in a range. Functions like sine or cosine map values from a domain of angles to a range of real values between -1 and +1. The details of the mapping are summarized in the name, domain, and range. We'll use this function concept as a way to package our Python programming into something that allows us to summarize the implementation details using a name.

We'll look at how to define and evaluate Python functions. In this chapter, we'll focus on Python functions that simply return Python objects as the range of values. In Chapter 8, More Advanced Functions, we'll look at generator functions; these are iterators, which are used with a for loop to produce sequences of values.

Python functions offer optional parameters as well as a mixture of positional and keyword parameters. This allows us to define a single function which has a number of variant signatures, allowing considerable flexibility...