12.2 Regular expressions

Suppose you post a question on an online software developer channel or website asking about some complex text search problem. Someone is likely to give a regular expression answer written as a combination of most of the letters and punctuation marks you can imagine.

Python’s engine to process the expression and find your text via regular expressions is in the re module. [PYR2] We also use regular expressions to perform sophisticated text substitutions.

Let’s begin by thinking about how we would find the substring "ecos" in

string = "Economic, ecological ecosystem"

Our process should return None if substring is not present in string. If it is, the function returns a tuple where the first item is the index of the first position at which it occurs, and the second is the length of the substring. We call this tuple the match information...