The use and difference of greedy and non-greedy patterns in Python's regular expressions

Regular expressions are not unique to Python, but are a set of independent grammars that are supported by many programming languages. The regular expression syntax used in different languages is not exactly the same, but broadly similar. This article focuses on the use and difference of greedy and non-greedy patterns. By default, regular expressions are matched in greedy mode, that is, to match as much of the content as possible to match. For example:

In the preceding code, the first \b in the regular expression represents a matching word header followed by a letter B that matches a word that begins with the letter B, followed by a dot. Indicates that any character (including spaces) is matched, and the plus sign + indicates that any preceding character appears one or more times, and the last \b represents the end of the word. So the question comes, what is the end of the word? Both whitespace and punctuation are counted at the end of the word, but the regular expression defaults to greedy mode, which matches as much content as possible, so the above code matches the end of the last word in the text.

How do you match a word that starts with the letter B instead of the one above? You can use non-greedy mode. Non-greedy mode is using the question mark "?" Complete, in a regular expression, if the question mark is preceded by a normal character or sub-pattern, the character or sub-pattern preceding the question mark may or may not appear. However, if the question mark follows the contents of +, * and {m,n}, it represents a non-greedy pattern, that is, matching as little content as possible. Take the above problem as an example and change to a non-greedy mode, for example:

The following code further demonstrates the difference between greedy and non-greedy modes:

Of course, back to the original question in this article, if just to match the word starting with the letter B, it is not so troublesome to use \w directly, because \w can only match letters, numbers, or underscores, and cannot match spaces. For example:

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