'Given a text, returns a list of the (start, end) spans of sentences
in the text.'

def span_tokenize(self, text, realign_boundaries=True):

    slices = self._slices_from_text(text)
    if realign_boundaries:
        slices = self._realign_boundaries(text, slices)
    return [(sl.start, sl.stop) for sl in slices]
