code: def except_keyword(source, start, keyword):
      
      start = pass_white(source, start)
      kl = len(keyword)  #keyword len
      if kl + start > len(source):
          return None
      if source[start:start + kl] != keyword:
          return None
      if kl + start < len(source) and source[start + kl] in IDENTIFIER_PART:
          return None
      return start + kl
docs: Returns position after keyword if found else None
          Note: skips white space