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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 subvolumes(self):
 """ Subvolumes contained in this mount. """

        self.SYNC()
        self._getDevices()
        self._getRoots()
        self._getMounts()
        self._getUsage()

        volumes = self.volumes.values()
        volumes.sort(key=(lambda v: v.fullPath))
        return volumes