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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 setSize(self, size, sizeIsEstimated):
 """ Update size. """

        self._size = size
        self._sizeIsEstimated = sizeIsEstimated

        if self.fromVol is not None and size is not None and not sizeIsEstimated:
            Diff.theKnownSizes[self.toUUID][self.fromUUID] = size