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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 config_schema(self):
 """Returns the merged configuration data schema for this plugin type."""

        from rez.config import _plugin_config_dict
        d = _plugin_config_dict.get(self.type_name, {})

        for name, plugin_class in self.plugin_classes.iteritems():
            if hasattr(plugin_class, "schema_dict") \
                    and plugin_class.schema_dict:
                d_ = {name: plugin_class.schema_dict}
                deep_update(d, d_)
        return dict_to_schema(d, required=True, modifier=expand_system_vars)