Pre-defining Named Recursive Subpatters In Regex

Note: I know none of this is supported in the existing re module, I am using the newer regex module intended to replace re in the future. I need to build some complex regular expre

Solution 1:

Since there is no syntax like the Perl/PCRE (?(DEFINE)....) in the new python regex module, you can use this trick (I think that it works in Ruby too):

import regex

pattern = r'''
  (?<userpart> thomas | richard | harold ){0}
  (?<domainpart> gmail | yahoo | hotmail ){0}
  (?<tld> com | net | co\.uk ){0}
  (?<email> (?&userpart)@(?&domainpart)\.(?&tld) ){0}

  ^ To: \s+ .* \s+ < (?&email) > $
'''

Since you add the quantifier {0}, you obtain zero width group definitions you can put everywhere.