code: def unirange(a, b):
      
      if b < a:
          raise ValueError("Bad character range")
      if a < 0x10000 or b < 0x10000:
          raise ValueError("unirange is only defined for non-BMP ranges")
  
      if sys.maxunicode > 0xffff:
          # wide build
          return u'[%s-%s]' % (unichr(a), unichr(b))
      else:
          # narrow build stores surrogates, and the 're' module handles them
          # (incorrectly) as characters.  Since there is still ordering among
          # these characters, expand the range to one that it understands.  Some
          # background in http://bugs.python.org/issue3665 and
          # http://bugs.python.org/issue12749
          #
          # Additionally, the lower constants are using unichr rather than
          # literals because jython [which uses the wide path] can't load this
          # file if they are literals.
          ah, al = _surrogatepair(a)
          bh, bl = _surrogatepair(b)
          if ah == bh:
              return u'(?:%s[%s-%s])' % (unichr(ah), unichr(al), unichr(bl))
          else:
              buf = []
              buf.append(u'%s[%s-%s]' %
                         (unichr(ah), unichr(al),
                          ah == bh and unichr(bl) or unichr(0xdfff)))
              if ah - bh > 1:
                  buf.append(u'[%s-%s][%s-%s]' %
                             unichr(ah+1), unichr(bh-1), unichr(0xdc00), unichr(0xdfff))
              if ah != bh:
                  buf.append(u'%s[%s-%s]' %
                             (unichr(bh), unichr(0xdc00), unichr(bl)))
  
              return u'(?:' + u'|'.join(buf) + u')'
docs: Returns a regular expression string to match the given non-BMP range.