Comparing item 2 and item 3, I think that item 3 is the Pythonic choice
and item 2 is a bad idea.

Item 4: back-references in the pattern are like \1 and (?P=name), not
\g<1> or \g<name>, and in the replacement string are like \g<1> and
\g<name>, not \1 (or  (?P=name)). I'd like to suggest that
back-references in the pattern also include \g<1> and \g<name> and
\g<-1> for relative back-references. Interestingly, Perl names groups
with (?<name>...) whereas Python uses (?P<name>...). A permissible
alternative?