Problem with qiskit version 0.33.0 related to the function measure

[andreamari]

Describe the bug
In the last version (0.33.0) of qiskit the function measure has been removed from qiskit.circuit.measure.
In pennylane_qiskit.qiskit_device.py there is however this line that now can create problems:

pennylane-qiskit/pennylane_qiskit/qiskit_device.py

Line 27 in 0998b85

from qiskit.circuit.measure import measure

To Reproduce
Note sure how to reproduce, but the problem shows up in a Mitiq PR unitaryfund/mitiq#1040.
See this line: https://github.com/unitaryfund/mitiq/runs/4442208499?check_suite_focus=true#step:6:2449

Possible Fix
Removing the import:

pennylane-qiskit/pennylane_qiskit/qiskit_device.py

Line 27 in 0998b85

from qiskit.circuit.measure import measure

and replacing

pennylane-qiskit/pennylane_qiskit/qiskit_device.py

Line 232 in 0998b85

measure(self._circuit, qr, cr)

with self._circuit.measure(qr, cr) may fix the problem. Not tested.

[CatalinaAlbornoz]

Hi @andreamari, thank you for pointing this out and for suggesting the fix!

[rmoyard]

Thanks @andreamari, I'll open a PR for the new version of Qiskit!

[jakelishman]

Apologies everyone - this shouldn't have been removed without a deprecation warning, and I'll add it back (with a deprecation warning) in Terra 0.19.1 later this week. The loose measure function here was never meant to be public; it was just a hold-over from how we used to build up the QuantumCircuit object with monkey-patching, and in a tidy-up for Terra 0.19 it got removed. The solution Andrea suggested is identical to the current code, and what the deprecation warning will suggest you do in the future. (Literally - the exact measure function you were importing was bound to QuantumCircuit.measure.)

See Qiskit/qiskit#7370 for our tracking issue on this.

[jakelishman]

Terra 0.19.1 and Qiskit 0.33.1 are live on PyPI now, which re-instated these functions with deprecation warnings.

[antalszava]

Thank you @jakelishman! 🙏