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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 tokens(self):
 """Return a list of token Spans for this sentence."""

        spans = self.word_tokenizer.span_tokenize(self.text)
        toks = [Token(
            text=self.text[span[0]:span[1]],
            start=span[0] + self.start,
            end=span[1] + self.start,
            lexicon=self.lexicon
        ) for span in spans]
        return toks