How to use the gprof2dot.UndefinedEvent function in gprof2dot

def prune(self, node_thres, edge_thres, paths, color_nodes_by_selftime):
        """Prune the profile"""

        # compute the prune ratios
        for function in compat_itervalues(self.functions):
            try:
                function.weight = function[TOTAL_TIME_RATIO]
            except UndefinedEvent:
                pass

            for call in compat_itervalues(function.calls):
                callee = self.functions[call.callee_id]

                if TOTAL_TIME_RATIO in call:
                    # handle exact cases first
                    call.weight = call[TOTAL_TIME_RATIO] 
                else:
                    try:
                        # make a safe estimate
                        call.weight = min(function[TOTAL_TIME_RATIO], callee[TOTAL_TIME_RATIO]) 
                    except UndefinedEvent:
                        pass

        # prune the nodes

def __getitem__(self, event):
        try:
            return self.events[event]
        except KeyError:
            raise UndefinedEvent(event)