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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _advance(self):
 """ Return the value of the current token and read the next one into self.cur_token. """

        cur_val = None if self.cur_token is None else self.cur_token.value
        try:
            self.cur_token = next(self._tokenizer)
        except StopIteration:
            self.cur_token = None
        return cur_val