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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 transform(self, offset):
 """ Shift this range by the specified offset. Note: the resulting range must be a valid interval. """

        assert self._start + offset > 0, \
            ('offset {} invalid; resulting range [{}, {}) is '
             'undefined'.format(offset, self._start+offset, self._end+offset))
        self._start += offset
        self._end += offset