def add_node(self, value):
        self.nodes.add(value)

    def add_edge(self, from_node, to_node, distance):
        if from_node == to_node:
            raise ValueError("Loop alert")
        if distance < 0:
            raise ValueError("Distance cannot be less than 0")
        self.edges[from_node].append(to_node)
        self.edges[to_node].append(from_node)
        if (from_node) not in self.nodes:
            self.nodes.add(from_node)
        if (to_node) not in self.nodes:
            self.nodes.add(to_node)
        self.distances[(from_node, to_node)] = distance
        self.distances[(to_node, from_node)] = distance