code: def except_token(source, start, token, throw=True):
      
      start = pass_white(source, start)
      if start < len(source) and source[start] == token:
          return start + 1
      if throw:
          raise SyntaxError('Missing token. Expected %s' % token)
      return None
docs: Token can be only a single char. Returns position after token if found. Otherwise raises syntax error if throw
      otherwise returns None