'Simple method to update the ranges.'

def set(self, start, stop, length=None, units='bytes'):

    assert is_byte_range_valid(start, stop, length), 'Bad    range    provided'
    self._units = units
    self._start = start
    self._stop = stop
    self._length = length
    if (self.on_update is not None):
        self.on_update(self)
