code: def separator(self, separator=",", end_token=None):
          
          while True:
              token = self.next()
              t_value = token["value"]
              if end_token and t_value == end_token:
                  raise self.ParseEnd()
              if t_value == separator:
                  return
              if t_value == "\n":
                  continue
              self.error("Unexpected character")
docs: Read through tokens till the required separator is found.  We ignore
          newlines.  If an end token is supplied raise a ParseEnd exception if it
          is found.