Deprecations

All PennyLane deprecations will raise a qml.PennyLaneDeprecationWarning. Pending and completed deprecations are listed below.

Pending deprecations

New operator arithmetic deprecations

The v0.36 release completes the main phase of PennyLane’s switchover to an updated approach for handling arithmetic operations between operators, check out the Updated operators page for more details. The old system is still accessible via disable_new_opmath(). However, the old system will be removed in an upcoming release and should be treated as deprecated. The following functionality will explicitly raise a deprecation warning when used:

  • op.ops and op.coeffs will be deprecated in the future. Use terms() instead.

    • Added and deprecated for Sum and Prod instances in v0.35

  • Accessing qml.ops.Hamiltonian is deprecated because it points to the old version of the class that may not be compatible with the new approach to operator arithmetic. Instead, using qml.Hamiltonian is recommended because it dispatches to the LinearCombination class when the new approach to operator arithmetic is enabled. This will allow you to continue to use qml.Hamiltonian with existing code without needing to make any changes.

    • Use of qml.ops.Hamiltonian is deprecated in v0.36

  • Accessing terms of a tensor product (e.g., op = X(0) @ X(1)) via op.obs is deprecated with new operator arithmetic. A user should use op.operands instead.

    • Deprecated in v0.36

Other deprecations

  • PennyLane Lightning and Catalyst will no longer support manylinux2014 (GLIBC 2.17) compatibile Linux operating systems, and will be migrated to manylinux_2_28 (GLIBC 2.28). See pypa/manylinux for additional details.

    • Last supported version of manylinux2014 with v0.36

    • Fully migrated to manylinux_2_28 with v0.37

  • MultiControlledX is the only controlled operation that still supports specifying control values with a bit string. In the future, it will no longer accepts strings as control values.

    • Deprecated in v0.36

    • Will be removed in v0.37

  • qml.from_qasm_file is deprecated. Instead, the user can open the file and then load its content using qml.from_qasm.

    >>> with open("test.qasm", "r") as f:
    ...     circuit = qml.from_qasm(f.read())
    
    • Deprecated in v0.36

    • Will be removed in v0.37

  • The qml.load function is a general-purpose way to convert circuits into PennyLane from other libraries. It is being deprecated in favour of the more specific functions from_qiskit, from_qasm, etc.

    • Deprecated in v0.36

    • Will be removed in v0.37

Completed deprecation cycles

  • single_tape_transform, batch_transform, qfunc_transform, op_transform, gradient_transform and hessian_transform are deprecated. Instead switch to using the new qml.transform function. Please refer to the transform docs to see how this can be done.

    • Deprecated in v0.34

    • Removed in v0.36

  • PauliWord and PauliSentence no longer use * for matrix and tensor products, but instead use @ to conform with the PennyLane convention.

    • Deprecated in v0.35

    • Removed in v0.36

  • The private functions _pauli_mult, _binary_matrix and _get_pauli_map from the pauli module have been removed, as they are no longer used anywhere and the same functionality can be achieved using newer features in the pauli module.

    • Deprecated in v0.35

    • Removed in v0.36

  • Calling qml.matrix without providing a wire_order on objects where the wire order could be ambiguous now raises an error. This includes tapes with multiple wires, QNodes with a device that does not provide wires, or quantum functions.

    • Deprecated in v0.35

    • Raises an error in v0.36

  • qml.pauli.pauli_mult and qml.pauli.pauli_mult_with_phase are now removed. Instead, you should use qml.simplify(qml.prod(pauli_1, pauli_2)) to get the reduced operator.

    >>> op = qml.simplify(qml.prod(qml.PauliX(0), qml.PauliZ(0)))
    >>> op
    -1j*(PauliY(wires=[0]))
    >>> [phase], [base] = op.terms()
    >>> phase, base
    (-1j, PauliY(wires=[0]))
    
    • Deprecated in v0.35

    • Removed in v0.36

  • MeasurementProcess.name and MeasurementProcess.data have been removed, as they contain dummy values that are no longer needed.

    • Deprecated in v0.35

    • Removed in v0.36

  • The contents of qml.interfaces is moved inside qml.workflow.

    • Contents moved in v0.35

    • Old import path removed in v0.36

  • The method Operator.validate_subspace(subspace), only employed under a specific set of qutrit operators, has been relocated to the qml.ops.qutrit.parametric_ops module and has been removed from the Operator class.

    • Deprecated in v0.35

    • Removed in v0.36

  • qml.transforms.one_qubit_decomposition and qml.transforms.two_qubit_decomposition are removed. Instead, you should use qml.ops.one_qubit_decomposition and qml.ops.two_qubit_decomposition.

    • Deprecated in v0.34

    • Removed in v0.35

  • Passing additional arguments to a transform that decorates a QNode should now be done through use of functools.partial. For example, the metric_tensor() transform has an optional approx argument which should now be set using:

    from functools import partial
    
    @partial(qml.metric_tensor, approx="block-diag")
    @qml.qnode(dev)
    def circuit(weights):
        ...
    

    The previously-recommended approach is now removed:

    @qml.metric_tensor(approx="block-diag")
    @qml.qnode(dev)
    def circuit(weights):
        ...
    

    Alternatively, consider calling the transform directly:

    @qml.qnode(dev)
    def circuit(weights):
        ...
    
    transformed_circuit = qml.metric_tensor(circuit, approx="block-diag")
    
    • Deprecated in v0.33

    • Removed in v0.35

  • Observable.return_type has been removed. Instead, you should inspect the type of the surrounding measurement process.

    • Deprecated in v0.34

    • Removed in v0.35

  • ClassicalShadow.entropy() no longer needs an atol keyword as a better method to estimate entropies from approximate density matrix reconstructions (with potentially negative eigenvalues) has been implemented.

    • Deprecated in v0.34

    • Removed in v0.35

  • QuantumScript.is_sampled and QuantumScript.all_sampled have been removed. Users should now validate these properties manually.

    from pennylane.measurements import *
    sample_types = (SampleMP, CountsMP, ClassicalShadowMP, ShadowExpvalMP)
    is_sample_type = [isinstance(m, sample_types) for m in tape.measurements]
    is_sampled = any(is_sample_type)
    all_sampled = all(is_sample_type)
    
    • Deprecated in v0.34

    • Removed in v0.35

  • qml.ExpvalCost has been removed. Users should use qml.expval() instead.

    @qml.qnode(dev)
    def cost_function(params):
        some_qfunc(params)
        return qml.expval(Hamiltonian)
    
    • Deprecated in v0.24

    • Removed in v0.35

  • Specifying control_values passed to qml.ctrl as a string is no longer supported.

    • Deprecated in v0.25

    • Removed in v0.34

  • qml.gradients.pulse_generator has become qml.gradients.pulse_odegen to adhere to paper naming conventions.

    • Deprecated in v0.33

    • Removed in v0.34

  • The prep keyword argument in QuantumScript has been removed. StatePrepBase operations should be placed at the beginning of the ops list instead.

    • Deprecated in v0.33

    • Removed in v0.34

  • The public methods of DefaultQubit are pending changes to follow the new device API.

    We will be switching to the new device interface in a coming release. In this new interface, simulation implementation details will be abstracted away from the device class itself and provided by composition, rather than inheritance. Therefore, some public and private methods from DefaultQubit will no longer exist, though its behaviour in a workflow will remain the same.

    If you directly interact with device methods, please consult pennylane.devices.Device and pennylane.devices.DefaultQubit for more information on what the new interface will look like and be prepared to make updates in a coming release. If you have any feedback on these changes, please create an issue or post in our discussion forum.

    • Deprecated in v0.31

    • Changed in v0.33

  • The behaviour of Operator.__eq__ and Operator.__hash__ has been updated. Their documentation has been updated to reflect the incoming changes.

    The changes to operator equality allow users to use operator equality the same way as with qml.equal. With the changes to hashing, unique operators that are equal now have the same hash. These changes now allow behaviour such as the following:

    >>> qml.RX(0.1, wires=0) == qml.RX(0.1, wires=0)
    True
    >>> {qml.PauliZ(0), qml.PauliZ(0)}
    {PauliZ(wires=[0])}
    

    Meanwhile, the previous behaviour is shown below:

    >>> qml.RX(0.1, wires=0) == qml.RX(0.1, wires=0)
    False
    >>> {qml.PauliZ(0), qml.PauliZ(0)}
    {PauliZ(wires=[0]), PauliZ(wires=[0])}
    
    • Added in v0.32

    • Behaviour changed in v0.33

  • qml.qchem.jordan_wigner had been removed. Use qml.jordan_wigner instead. List input to define the fermionic operator is no longer accepted; the fermionic operators qml.FermiA, qml.FermiC, qml.FermiWord and qml.FermiSentence should be used instead. See the pennylane.fermi module documentation and the Fermionic Operator tutorial for more details.

    • Deprecated in v0.32

    • Removed in v0.33

  • The tuple input type in qubit_observable has been removed. Please use a fermionic operator object. The tuple return type in fermionic_hamiltonian and fermionic_observable has been removed and these functions will return a fermionic operator by default.

    • Deprecated in v0.32

    • Removed in v0.33

  • The sampler_seed argument of qml.gradients.spsa_grad has been removed. Instead, the sampler_rng argument should be set, either to an integer value, which will be used to create a PRNG internally, or to a NumPy pseudo-random number generator (PRNG) created via np.random.default_rng(seed). The advantage of passing a PRNG is that one can reuse that PRNG when calling spsa_grad multiple times, for instance during an optimization procedure.

    • Deprecated in v0.32

    • Removed in v0.33

  • The RandomLayers.compute_decomposition keyword argument ratio_imprivitive has been changed to ratio_imprim to match the call signature of the operation.

    • Deprecated in v0.32

    • Removed in v0.33

  • The QuantumScript.set_parameters method and the QuantumScript.data setter have been removed. Please use QuantumScript.bind_new_parameters instead.

    • Deprecated in v0.32

    • Removed in v0.33

  • The observables argument in QubitDevice.statistics is removed. Please use circuit instead. Using a list of observables in QubitDevice.statistics is removed. Please use a QuantumTape instead.

    • Still accessible in v0.28-v0.31

    • Removed in v0.32

  • The CV observables qml.X and qml.P have been removed. Use qml.QuadX and qml.QuadP instead.

    • Deprecated in v0.32

    • Removed in v0.33

  • The method tape.unwrap() and corresponding UnwrapTape and Unwrap classes are removed.

    • Deprecated in v0.32

    • Removed in v0.33

    Instead of tape.unwrap(), use convert_to_numpy_parameters():

    from pennylane.transforms import convert_to_numpy_parameters
    
    qscript = qml.tape.QuantumTape([qml.RX(torch.tensor(0.1234), 0)],
                                     [qml.expval(qml.Hermitian(torch.eye(2), 0))] )
    unwrapped_qscript = convert_to_numpy_parameters(qscript)
    
    torch_params = qscript.get_parameters()
    numpy_params = unwrapped_qscript.get_parameters()
    
  • qml.enable_return and qml.disable_return have been removed. The old return types are no longer available.

    • Deprecated in v0.32

    • Removed in v0.33

  • The mode keyword argument in QNode has been removed, as it was only used in the old return system (which has also been removed). Please use grad_on_execution instead.

    • Deprecated in v0.32

    • Removed in v0.33

  • qml.math.purity, qml.math.vn_entropy, qml.math.mutual_info, qml.math.fidelity, qml.math.relative_entropy, and qml.math.max_entropy no longer support state vectors as input. Please call qml.math.dm_from_state_vector on the input before passing to any of these functions.

    • Still accepted in v0.31

    • Removed in v0.32

  • The do_queue keyword argument in qml.operation.Operator has been removed. This affects all child classes, such as Operation, Observable, SymbolicOp and more. Instead of setting do_queue=False, use the qml.QueuingManager.stop_recording() context.

    • Deprecated in v0.31

    • Removed in v0.32

  • The qml.specs dictionary longer supports direct key access to certain keys. Instead these quantities can be accessed as fields of the new Resources object saved under specs_dict["resources"]:

    • num_operations is no longer supported, use specs_dict["resources"].num_gates

    • num_used_wires is no longer supported, use specs_dict["resources"].num_wires

    • gate_types is no longer supported, use specs_dict["resources"].gate_types

    • gate_sizes is no longer supported, use specs_dict["resources"].gate_sizes

    • depth is no longer supported, use specs_dict["resources"].depth

    These keys were still accessible in v0.31 and removed in v0.32.

  • qml.math.reduced_dm has been removed. Please use qml.math.reduce_dm or qml.math.reduce_statevector instead.

    • Still accessible in v0.31

    • Removed in v0.32

  • QuantumScript’s name keyword argument and property are removed. This also affects QuantumTape and OperationRecorder.

    • Deprecated in v0.31

    • Removed in v0.32

  • The Operation.base_name property is removed. Please use Operator.name or type(obj).__name__ instead.

    • Still accessible in v0.31

    • Removed in v0.32

  • LieAlgebraOptimizer has been renamed. Please use RiemannianGradientOptimizer instead.

    • Deprecated in v0.31

    • Removed in v0.32

  • The grouping_type and grouping_method arguments of qchem.molecular_hamiltonian() are removed.

    • Deprecated in v0.31

    • Removed in v0.32

    Instead, simply construct a new instance of Hamiltonian with the grouping specified:

    H, qubits = molecular_hamiltonian(symbols, coordinates)
    grouped_h = qml.Hamiltonian(
        H.coeffs,
        H.ops,
        grouping_type=grouping_type,
        groupingmethod=grouping_method,
    )
    
  • zyz_decomposition and xyx_decomposition are removed, use one_qubit_decomposition with a rotations keyword instead.

    • Deprecated in v0.31

    • Removed in v0.32

  • The qml.utils.sparse_hamiltonian function has been removed. ~.Hamiltonian.sparse_matrix should be used instead.

    • Deprecated in v0.29

    • Removed in v0.31

  • The collections module has been removed.

    • Deprecated in v0.29

    • Removed in v0.31

  • qml.op_sum has been removed. Users should use qml.sum instead.

    • Deprecated in v0.29.

    • Removed in v0.31.

  • The argument argnum for gradient transforms using the Jax interface is replaced by argnums.

    • argnum is automatically changed to argnums for gradient transforms using JAX and a warning is raised in v0.30

    • argnums is the only option for gradient transforms using JAX in v0.31

  • Evolution now adds a -1 to the input parameter. Beforehand, the minus sign was not included.

    • Transition warning added in v0.29.

    • Updated to current behaviour in v0.30.

  • The seed_recipes argument in qml.classical_shadow and qml.shadow_expval has been removed. An argument seed which defaults to None can contain an integer with the wanted seed.

    • Still accessible in v0.28, v0.29

    • Removed in v0.30

  • The get_operation tape method is updated to return the operation index as well, changing its signature.

    • The new signature is available by changing the arg return_op_index to True in v0.29

    • The old signature is replaced with the new one in v0.30

  • The grouping module has been removed. The functionality has been moved and reorganized in the new pauli module under pauli/utils.py or pauli/grouping/.

    • Still accessible in v0.27, v0.28, v0.29, v0.30

    • Removed in v0.31

    The functions from grouping/pauli.py, grouping/transformations.py and grouping/utils.py have been moved to pauli/utils.py. The remaining functions have been consolidated in the pauli/grouping/ directory.

  • qml.VQECost is removed.

    • Deprecated in 0.13

    • Removed in 0.29

  • In-place inversion — op.inv() and op.inverse=value — is deprecated. Please use qml.adjoint or qml.pow instead.

    • Still accessible in v0.27 and v0.28

    • Removed in v0.29

    Don’t use:

    >>> v1 = qml.PauliX(0).inv()
    >>> v2 = qml.PauliX(0)
    >>> v2.inverse = True
    

    Instead, use:

    >>> qml.adjoint(qml.PauliX(0))
    Adjoint(PauliX(wires=[0]))
    >>> qml.pow(qml.PauliX(0), -1)
    PauliX(wires=[0])**-1
    >>> qml.pow(qml.PauliX(0), -1, lazy=False)
    PauliX(wires=[0])
    >>> qml.PauliX(0) ** -1
    PauliX(wires=[0])**-1
    
  • The qml.utils.decompose_hamiltonian() method is removed. Please use qml.pauli_decompose().

    • Still accessible in v0.27

    • Removed in v0.28

  • qml.tape.get_active_tape is deprecated. Please use qml.QueuingManager.active_context() instead.

    • Deprecated in v0.27

    • Removed in v0.28

  • qml.transforms.qcut.remap_tape_wires is deprecated. Please use qml.map_wires instead.

    • Deprecated in v0.27

    • Removed in v0.28

  • QuantumTape.inv() is deprecated. Please use QuantumTape.adjoint() instead. This method returns a new tape instead of modifying itself in-place.

    • Deprecated in v0.27

    • Removed in v0.28

  • qml.tape.stop_recording and QuantumTape.stop_recording are moved to qml.QueuingManager.stop_recording

    • Deprecated in v0.27

    • Removed in v0.28

  • QueuingContext is renamed QueuingManager.

    • Deprecated name QueuingContext in v0.27

    • Removed in v0.28

  • QueuingManager.safe_update_info and AnnotateQueue.safe_update_info are removed.

    • Deprecated in v0.27

    • Removed in v0.28

  • ObservableReturnTypes Sample, Variance, Expectation, Probability, State, and MidMeasure are moved to measurements from operation.

    • Deprecated in v0.23

    • Removed in v0.27

  • The qml.utils.expand function is deprecated. qml.math.expand_matrix should be used instead.

    • Deprecated in v0.24

    • Removed in v0.27

  • The qml.Operation.get_parameter_shift method is removed. Use the methods of the gradients module for general parameter-shift rules instead.

    • Deprecated in v0.22

    • Removed in v0.28

  • qml.transforms.measurement_grouping has been removed. Please use qml.transforms.hamiltonian_expand instead.

    • Deprecated in v0.28

    • Removed in v0.29

  • qml.transforms.make_tape was previously deprecated, but there is no longer a plan to remove it. It no longer raises a warning, and the functionality is unchanged.

    • Deprecated in v0.28

    • Un-deprecated in v0.29