Parameter assignment of QuantumCircuitdoes not update the data attribute when inplace=True

[arthurostrauss]

Environment

• Qiskit version: 1.2.4
• Python version: 3.10
• Operating system: Mac OS Sequoia

What is happening?

When writing the following:

import numpy as np

from qiskit.circuit.library import TwoLocal

num_qubits = 6
n_layers = 4

qc = TwoLocal(num_qubits, "rx", "cx", entanglement=[[(0, 1), (2, 3), (4, 5)], [(1, 2), (3, 4)]], reps=n_layers, flatten=True, skip_unentangled_qubits=True, skip_final_rotation_layer=True)
qc.assign_parameters(rotation_angles, inplace=True)
print(qc.data)

we get:

[CircuitInstruction(operation=Instruction(name='rx', num_qubits=1, num_clbits=0, params=[ParameterVectorElement(θ[0])]), qubits=(Qubit(QuantumRegister(6, 'q'), 0),), clbits=()), CircuitInstruction(operation=Instruction(name='rx', num_qubits=1, num_clbits=0, params=[ParameterVectorElement(θ[1])]), ...]

Meaning that instructions still store the reference to the original Parameters, which should have been replaced by the values.

This behavior does not appear when doing

qc=qc.assign_parameters(rotation_angles, inplace=False)

where in this case the binding is clearly visible on the instructions

How can we reproduce the issue?

import numpy as np

from qiskit.circuit.library import TwoLocal

num_qubits = 6
n_layers = 4

qc = TwoLocal(num_qubits, "rx", "cx", entanglement=[[(0, 1), (2, 3), (4, 5)], [(1, 2), (3, 4)]], reps=n_layers, flatten=True, skip_unentangled_qubits=True, skip_final_rotation_layer=True)

rotation_angles = np.random.random(qc.num_parameters)
qc.assign_parameters(rotation_angles, inplace=True)
print(qc.data)

What should happen?

Instructions should be binded with the numeric values in both cases. One should therefore take care of the inplace=True case to match the other case.

Any suggestions?

No response

[Cryoris]

It looks like this is caused by the caching of Python gates in the Rust-side CircuitData. Likely the cache is not properly cleared and the gate re-uses the old definition. Until we fix this, you can turn the caching off by installing Qiskit from source and then do

export QISKIT_NO_CACHE_GATES=1   <-- tell Qiskit not to cache gates
python setup.py build_rust --inplace --release  <-- rebuild Rust in release mode

Edit: This only happens with flatten=True. Using a plain circuit or using flatten=False followed by .decompose() does not raise this. Maybe flatten=True somehow builds an inconsistent/incompatible state...