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Regular expressions offer a powerful way of searching texts for strings that match a particular pattern, and for replacing such strings with other strings which themselves can depend on what was matched.

In this chapter we saw that most characters are matched literally and are implicitly quantified by {1}. We also learned how to specify character classes—sets of characters to match—and how to negate such sets and include ranges of characters in them without having to write each character individually.

We learned how to quantify expressions to match a specific number of times or to match from a given minimum to a given maximum number of times, and how to use greedy and nongreedy matching. We also learned how to group one or more expressions together so that they can be quantified (and optionally captured) as a unit.

The chapter also showed how what is matched can be affected by using various assertions, such as positive and negative lookahead and lookbehind, and by various flags, for example, to control the interpretation of the period and whether to use case-insensitive matching.

The final section showed how to put regexes to use within the context of Python programs. In this section we learned how to use the functions provided by the re module, and the methods available from compiled regexes and from match objects. We also learned how to replace matches with literal strings, with literal strings that contain backreferences, and with the results of function calls or lambda expressions, and how to make regexes more maintainable by using named captures and comments.

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