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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 get_disk_usage(self, path=None):
 """Return the total, used and free disk space in bytes as named tuple, or placeholder values simulating unlimited space if not set. .. note:: This matches the return value of shutil.disk_usage(). Args: path: The disk space is returned for the file system device where `path` resides. Defaults to the root path (e.g. '/' on Unix systems). """

        DiskUsage = namedtuple('usage', 'total, used, free')
        if path is None:
            mount_point = self.mount_points[self.root.name]
        else:
            mount_point = self._mount_point_for_path(path)
        if mount_point and mount_point['total_size'] is not None:
            return DiskUsage(mount_point['total_size'],
                             mount_point['used_size'],
                             mount_point['total_size'] -
                             mount_point['used_size'])
        return DiskUsage(
            1024 * 1024 * 1024 * 1024, 0, 1024 * 1024 * 1024 * 1024)