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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 add_lv_load_area(self, lv_load_area):
 """ Adds a Load Area `lv_load_area` to _lv_load_areas if not already existing Additionally, adds the associated centre object to MV grid's _graph as node. Args ---- lv_load_area: LVLoadAreaDing0 instance of class LVLoadAreaDing0 """

        if lv_load_area not in self.lv_load_areas() and isinstance(lv_load_area, LVLoadAreaDing0):
            self._lv_load_areas.append(lv_load_area)
            self.mv_grid.graph_add_node(lv_load_area.lv_load_area_centre)