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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 plotter_cls(self):
 """The plotter class"""

        ret = self._plotter_cls
        if ret is None:
            self._logger.debug('importing %s', self.module)
            mod = import_module(self.module)
            plotter = self.plotter_name
            if plotter not in vars(mod):
                raise ImportError("Module %r does not have a %r plotter!" % (
                    mod, plotter))
            ret = self._plotter_cls = getattr(mod, plotter)
            _versions.update(get_versions(key=lambda s: s == self._plugin))
        return ret