Whenever you call one of the regular expression methods, the engine has to convert the pattern string into an internal structure that makes searching strings fast. This conversion takes a non-trivial amount of time. If a regular expression pattern is going to be reused multiple times (for example, inside a for or while loop), it would be better if this conversion step could be done only once.
This is possible with the re.compile method. It returns an object-oriented version of the regular expression that has been compiled down and has the methods we've explored (match, search, and findall) already, among others. We'll see examples of this in the case study.
This has definitely been a condensed introduction to regular expressions. At this point, we have a good feel for the basics and will recognize when we need to do further research. If we have a string pattern-matching problem, regular expressions will almost certainly be able to solve them for us. However, we may need to look up new syntaxes in a more comprehensive coverage of the topic. But now we know what to look for! Let's move on to a completely different topic: filesystem paths.