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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 execution_engine_model_changed(self, model, prop_name, info):
 """High light active state machine. """


        notebook = self.view['notebook']
        active_state_machine_id = self.model.state_machine_manager.active_state_machine_id

        if active_state_machine_id is None:
            # un-mark all state machine that are marked with execution-running style class
            for tab in self.tabs.values():
                label = notebook.get_tab_label(tab['page']).get_child().get_children()[0]
                if label.get_style_context().has_class(constants.execution_running_style_class):
                    label.get_style_context().remove_class(constants.execution_running_style_class)
        else:
            # mark active state machine with execution-running style class
            page = self.get_page_for_state_machine_id(active_state_machine_id)
            if page:
                label = notebook.get_tab_label(page).get_child().get_children()[0]
                label.get_style_context().add_class(constants.execution_running_style_class)