def METHOD_NAME(self, current_char):
    if current_char in ('"', "'"):
        return self._open_quoted_string(current_char)
    elif current_char.isspace():
        return self._close_current_token(current_char)
    elif current_char == '(':
        return self._open_paren(current_char)
    elif current_char == ')':
        return self._close_paren(current_char)
    else:
        self._current_token += current_char
    return None