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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 coverage(self):
 """ Get the fraction of this title sequence that is matched by its reads. @return: The C{float} fraction of the title sequence matched by its reads. """

        intervals = ReadIntervals(self.subjectLength)
        for hsp in self.hsps():
            intervals.add(hsp.subjectStart, hsp.subjectEnd)
        return intervals.coverage()