class NodeAdd(PortNode):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.description = "Perform the addition of the two input port values."

        self.add_input_port("a")
        self.add_input_port("b")
        self.add_output_port("output")

    def process(self):
        a = self.get_input("a")
        b = self.get_input("b")

        if a is None or b is None:
            return

        self._output_ports["output"].value = a + b

        self.dirty = False

class NodeMultiply(PortNode):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.description = (
            "Perform the multiplication of the two input port values."
        )

        self.add_input_port("a")
        self.add_input_port("b")
        self.add_output_port("output")

    def process(self):
        a = self.get_input("a")
        b = self.get_input("b")

        if a is None or b is None:
            return

        self._output_ports["output"].value = a * b

        self.dirty = False

node_add = NodeAdd()
node_add.set_input("a", 1)
node_add.set_input("b", 1)
node_multiply = NodeMultiply()
node_multiply.set_input("b", 2)

graph = PortGraph()

graph.add_node(node_add)
graph.add_node(node_multiply)

graph.connect(node_add, "output", node_multiply, "a")

graph.process()

print(node_multiply.get_output("output"))
graph.to_graphviz().draw("Graph.png", prog="dot")