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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 update_global_variables_list_store(self):
 """Updates the global variable list store Triggered after creation or deletion of a variable has taken place. """

        # logger.info("update")
        self.list_store_iterators = {}
        self.list_store.clear()
        keys = self.model.global_variable_manager.get_all_keys()
        keys.sort()
        for key in keys:
            iter = self.list_store.append([key,
                                           self.model.global_variable_manager.get_data_type(key).__name__,
                                           str(self.model.global_variable_manager.get_representation(key)),
                                           str(self.model.global_variable_manager.is_locked(key)),
                                           ])
            self.list_store_iterators[key] = iter