I think it is a bug but I'm not really sure. Basically, what I'm trying to do is the following: I have an Oracle Instruction which I want to append to my QuantumCircuit, looks as follows:
# initialising registers for readability
[control, train_register] = circ.qregs
circ.h(control)
# create and append oracle
oracle = create_oracle(train_register, control) # returns an Instruction
circ.append(oracle, [train_register, control])
If my train_register and control are both QuantumRegisters with length 1, this works perfectly fine. But I want to make this work for variable length of these registers, I get the error qiskit.circuit.exceptions.CircuitError: 'The amount of qubit arguments does not match the instruction expectation.'.
This is logical, since this error occurs because qiskit checks the length of my provided qargs in QuantumCircuit.append(), and I provided two registers in a list with both one qubit, so the length of the list happens to be the same as the number of qubits.
However, I want this to work for variable length. If I know what the length of my QuantumRegisters are, say len(train_register) is 3 and len(control) is 1 I can use
circ.append(oracle, [0, 1, 2, 3])
Or to make it work for unspecified lengths, I can write something like:
indices_to_append_to = list(np.arange(len(train_register) + len(control)))
circ.append(oracle, indices_to_append_to)
But I just really like the idea of just plugging in the names of the qregs as qargs. Is there something to make this work like that?
