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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 _get_tokens_dict(self):
 """ Accesses tokens dict :return: The ordered dict of the tokens :rtype: collections.OrderedDict """

        if self._tokens_dict is None:
            tokens = [Token(element) for element in self._element.xpath('tokens/token')]
            self._tokens_dict = OrderedDict([(t.id, t) for t in tokens])
        return self._tokens_dict