code: def _combined_regex(regexes, flags=re.IGNORECASE, use_re2=False, max_mem=None):
      
      joined_regexes = "|".join(r for r in regexes if r)
      if not joined_regexes:
          return None
  
      if use_re2:
          import re2
          return re2.compile(joined_regexes, flags=flags, max_mem=max_mem)
      return re.compile(joined_regexes, flags=flags)
docs: Return a compiled regex combined (using OR) from a list of ``regexes``.
      If there is nothing to combine, None is returned.
  
      re2 library (https://github.com/axiak/pyre2) often can match and compile
      large regexes much faster than stdlib re module (10x is not uncommon),
      but there are some gotchas:
  
      * in case of "DFA out of memory" errors use ``max_mem`` argument
        to increase the amount of memory re2 is allowed to use.