This was a long chapter! We've covered a lot of material in it. We began with how strings work in Python and their different notations in Python 2.x and Python 3.x. After that, we looked at how to build regular expressions, the objects and interface the re module give us to deal with them, and the most important operations for searching and modifying strings. We also learned how to extract information from a pattern through MatchObject, such as the position or the groups of a match. We also learned how to modify the default behavior of some character classes and metacharacters using the compilation flags. And finally, we've seen how to deal with Unicode and the new features we can find in Python 3.x.
Throughout this chapter, we've seen that groups are crucial part of regular expressions and that many operations of the re module are meant to be used with groups. That's why we cover groups in depth in the following chapter.