django url (?P<>) regex - named capture group and backreference

Nearly all modern regular expression engines support numbered capturing groups and numbered backreferences. Long regular expressions with lots of groups and backreferences may be hard to read. They can be particularly difficult to maintain as adding or removing a capturing group in the middle of the regex upsets the numbers of all the groups that follow the added or removed group.

Python's re module was the first to offer a solution: named capturing groups and named backreferences.

(?P<name>group)

captures the match of group into the backreference "name". name must be an alphanumeric sequence starting with a letter. group can be any regular expression. You can reference the contents of the group with the named backreference

(?P=name)

. The question mark, P, angle brackets, and equals signs are all part of the syntax. Though the syntax for the named backreference uses parentheses, it's just a backreference that doesn't do any capturing or grouping.