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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 span_tokenize(self, s):
 """Return a list of integer offsets that identify sentences in the given text. :param string s: The text to tokenize into sentences. :rtype: iter(tuple(int, int)) """

        if self._tokenizer is None:
            self._tokenizer = load_model(self.model)
        # for debug in tokenizer.debug_decisions(s):
        #     log.debug(format_debug_decision(debug))
        return self._tokenizer.span_tokenize(s)