正则表达式中`？：`的含义是什么？

Question

I saw a regular expression to match a URL: /^\\/users?(?:\\/(\\d+)(?:\\.\\.(\\d+))?)?/ . I am confused by the usage of ?: in the beginning of each group match.

What's the meaning of that?

Answer 1

(?:) (the () are part of the expression) is a non-capturing group .

See http://www.regular-expressions.info/refadv.html .

Answer 2

It's a non-capturing group, so if a match is made that particular group will not be captured.

http://www.regular-expressions.info/refadv.html

Answer 3

Read through: http://docs.python.org/library/re.html

(?:...)

A non-capturing version of regular parentheses. Matches whatever regular expression is inside the parentheses, but the substring matched by the group cannot be retrieved after performing a match or referenced later in the pattern.