An implementation idea for the Gate hierarchy of QISKit

qiskit_gate_idea.py

# Base class for each gate
class Gate:
    def __init__(self, name: str, qubits):
        self._name = name
        if isinstance(qubits, list):
            self._qubits = qubits
        else:
            self._qubits = [qubits]
            
    def qasm(self) -> str:
        return "{} {}".format(self._name, ",".join(self._registers))
    # Other methods

# Base class for reversible gates
class ReversibleGate(Gate):
    def inverse(self):
        raise NotImplementedError("You should redefine the inverse() function "
                                  "for each ReversibleGate.")

# Base class for custom gates
class CompositeGateBase(Gate):
    def __init__(self, name: str, registers):
        super().__init__(name, registers)
        self._gate_list = list()
        
    def append(self, gate):
        self._gate_list.append(gate)

    # Operator +=
    def __iadd__(self, gate: Gate):
        self.append(gate)

class CompositeGate(CompositeGateBase):
    def __init__(self, name: str, qubits):
        super().__init__(name, qubits)
        
class ReversibleCompositeGate(CompositeGateBase):
    def __init__(self, name: str, qubits):
        super().__init__(name, qubits)
        self._gate_list = list()
        
    def inverse(self):
        self._gate_list = [gate.inverse() for gate in reversed(self._gate_list)]
        return self

# Base gate implementation example
class HGate(ReversibleGate):
    def __init__(self, qubit):
        super().__init__("H", qubit)

    def inverse(self):
        return HGate(self._qubits)

class CNOTGate(ReversibleGate):
    def __init__(self, control, target):
        super().__init__("CNOT", [control, target])

    def inverse(self):
        return CNOTGate(*self._qubits)

# Custom gate definition
class MyCustomGate(ReversibleCompositeGate):
    def __init__(self, qbyte):
        for i in range(len(qbyte)):
            self += HGate(qbyte[i])
        self += CNOTGate(qbyte[0], qbyte[1])

# Custom gate creation at runtime
qbyte = [("qreg", i) for i in range(8)]
my_custom_gate = ReversibleCompositeGate("MyCustomGate", qbyte)
for i in range(len(qbyte)):
    my_custom_gate += HGate(qbyte[i])
my_custom_gate += CNOTGate(qbyte[0], qbyte[1])