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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 _keepVol(self, vol):
 """ Mark this volume to be kept in path. """

        if vol is None:
            return

        if vol in self.extraVolumes:
            del self.extraVolumes[vol]
            return

        if vol not in self.paths:
            raise Exception("%s not in %s" % (vol, self))

        paths = [os.path.basename(path) for path in self.paths[vol]]
        newPath = self.selectReceivePath(paths)

        if self._skipDryRun(logger, 'INFO')("Copy %s to %s", vol, newPath):
            return

        self.butterVolumes[vol.uuid].copy(newPath)