Python 3 Object-Oriented Programming - Third Edition

Grouping patterns together

So far, we've seen how we can repeat a pattern multiple times, but we are restricted in what patterns we can repeat. If we want to repeat individual characters, we're covered, but what if we want a repeating sequence of characters? Enclosing any set of patterns in parentheses allows them to be treated as a single pattern when applying repetition operations. Compare these patterns:

'abccc' matches pattern 'abc{3}'
'abccc' does not match pattern '(abc){3}'
'abcabcabc' matches pattern '(abc){3}'  

Combined with complex patterns, this grouping feature greatly expands our pattern-matching repertoire. Here's a regular expression that matches simple English sentences:

'Eat.' matches pattern '[A-Z][a-z]*( [a-z]+)*\.$'