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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 seq_site_length(self):
 """Calculate length of a single sequence site based upon relative positions specified in peak descriptions. :return: Length of sequence site. :rtype: :py:class:`int` """

        relative_positions_set = set()
        for peak_descr in self:
            relative_positions_set.update(peak_descr.relative_positions)
        return len(relative_positions_set)