Logic gate classes - how exactly does the flow of execution work here?

Question

I have a LogicGate class, which can have one or two input lines ( UnaryGate and BinaryGate subclasses, respectively) and a Connector class, which contains two LogicGate objects and has a method that returns one gate's output to another so the gate at the receiving end can perform operations on it. What I'm having trouble understanding is what object is actually performing the get_from() method here:

class LogicGate:

    def __init__(self,n):
        self.label = n
        self.output = None

    def get_label(self):
        return self.label

    def get_output(self):
        self.output = self.perform_gate_logic()
        return self.output

class UnaryGate(LogicGate):

    def __init__(self,n):
        LogicGate.__init__(self,n)

        self.pin = None

    def get_pin(self):
        if self.pin == None:
            pin = int(input("Enter Pin input for gate " + self.get_label() + "-->"))
            while pin != 1 and pin != 0:
                pin = int(input("Try again with 1 or 0 -->"))
            return pin
        else:
            return self.pin.get_from().get_output()

    def set_next_pin(self,source):
        if self.pin == None:
            self.pin = source
        else:
            raise RuntimeError("ERROR: NO EMPTY PINS")

class Connector:

    def __init__(self,fgate,tgate):
        self.fromgate = fgate
        self.togate = tgate

        tgate.set_next_pin(self)

    def get_from(self):
        return self.fromgate

    def get_to(self):
        return self.togate

What exactly is self.pin.get_from().get_output() doing in the get_pin() method? If the UnaryGate performing get_pin() is the Connector 's togate , then get_from() returns the corresponding fromgate , which in turn performs get_output() and returns 1 or 0 based on the input it received from the one or two gates it's connected to. What I can't wrap my head around is the self.pin.get_from() part. Is get_from() being invoked on a pin object, which to my understanding is just a class attribute that can be 1 , 0 or None ? That doesn't make much sense to me as I don't see how it could perform the method. How exactly is the data 'transferred' between a gate and the gate(s) it's connected to?

Answer 1

When the gate hasn't received any input from the user, the pins are actually connectors, as shown by this interpreter session:

>>> g1 = AndGate("g1")
>>> g2 = AndGate("g2")
>>> g3 = OrGate("g3")
>>> g4 = NotGate("g4")
>>> c1 = Connector(g1,g3)
>>> c2 = Connector(g2,g3)
>>> c3 = Connector(g3,g4)
>>> repr(g4)
'<__main__.NotGate object at 0x102958890>'
>>> g4.pin
<__main__.Connector object at 0x10297f450>
>>> g4.pin == c3
True
>>> g3.pin_a
<__main__.Connector object at 0x10297f590>
>>> g3.pin_a == c1
True
>>> g3.pin_b == c2
True
>>> g1.pin_a
>>> print(g1.pin_a)
None
>>> 

Now I understand how they can perform the method.