Remove deprecated old transform functionalities

doc/development/deprecations.rst

@@ -43,14 +43,6 @@ Pending deprecations
   - Deprecated in v0.35
   - Will raise an error in v0.36
 
-* ``single_tape_transform``, ``batch_transform``, ``qfunc_transform``, and ``op_transform`` are
-  deprecated. Instead switch to using the new ``qml.transform`` function. Please refer to
-  `the transform docs <https://docs.pennylane.ai/en/stable/code/qml_transforms.html#custom-transforms>`_
-  to see how this can be done.
-
-  - Deprecated in v0.34
-  - Will be removed in v0.36
-
 * ``PauliWord`` and ``PauliSentence`` no longer use ``*`` for matrix and tensor products,
   but instead use ``@`` to conform with the PennyLane convention.
 
@@ -64,6 +56,15 @@ Pending deprecations
 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 <https://docs.pennylane.ai/en/stable/code/qml_transforms.html#custom-transforms>`_
+  to see how this can be done.
+
+  - Deprecated in v0.34
+  - Removed in v0.36
+
 * ``MeasurementProcess.name`` and ``MeasurementProcess.data`` have been deprecated, as they contain
   dummy values that are no longer needed.
 

doc/releases/changelog-dev.md

@@ -62,6 +62,12 @@
 * The contents of ``qml.interfaces`` is moved inside ``qml.workflow``. The old import path no longer exists.
   [(#5329)](https://github.com/PennyLaneAI/pennylane/pull/5329)
 
+* ``single_tape_transform``, ``batch_transform``, ``qfunc_transform``, ``op_transform``, `` gradient_transform``
+  and ``hessian_transform`` are removed. Instead, switch to using the new ``qml.transform`` function. Please refer to
+  `the transform docs <https://docs.pennylane.ai/en/stable/code/qml_transforms.html#custom-transforms>`_
+  to see how this can be done.
+  [(#5339)](https://github.com/PennyLaneAI/pennylane/pull/5339)
+
 <h3>Deprecations 👋</h3>
 
 * ``qml.load`` is deprecated. Instead, please use the functions outlined in the *Importing workflows* quickstart guide, such as ``qml.from_qiskit``.

pennylane/__init__.py

@@ -90,9 +90,6 @@
     compile,
     defer_measurements,
     dynamic_one_shot,
-    qfunc_transform,
-    op_transform,
-    single_tape_transform,
     quantum_monte_carlo,
     apply_controlled_Q,
     commutation_dag,

pennylane/gradients/__init__.py

@@ -338,8 +338,7 @@ def my_custom_gradient(tape: qml.tape.QuantumTape, **kwargs) -> (Sequence[qml.ta
 from . import pulse_gradient
 from . import pulse_gradient_odegen
 
-from .gradient_transform import gradient_transform, SUPPORTED_GRADIENT_KWARGS
-from .hessian_transform import hessian_transform
+from .gradient_transform import SUPPORTED_GRADIENT_KWARGS
 from .finite_difference import finite_diff, finite_diff_coeffs
 from .parameter_shift import param_shift
 from .parameter_shift_cv import param_shift_cv

pennylane/gradients/gradient_transform.py

@@ -18,7 +18,6 @@
 import warnings
 
 import pennylane as qml
-from pennylane.transforms.tape_expand import expand_invalid_trainable
 from pennylane.measurements import (
     MutualInfoMP,
     StateMP,
@@ -441,156 +440,3 @@ def _reshape(x):
     if not cjac_is_tuple:
         return tuple(tdot(qml.math.stack(q), qml.math.stack(cjac)) for q in qjac)
     return tuple(tuple(tdot(qml.math.stack(q), c) for c in cjac if c is not None) for q in qjac)
-
-
-class gradient_transform(qml.batch_transform):  # pragma: no cover
-    """Decorator for defining quantum gradient transforms.
-
-    Quantum gradient transforms are a specific case of :class:`~.batch_transform`.
-    All quantum gradient transforms accept a tape, and output
-    a batch of tapes to be independently executed on a quantum device, alongside
-    a post-processing function that returns the result.
-
-    Args:
-        expand_fn (function): An expansion function (if required) to be applied to the
-            input tape before the gradient computation takes place. If not provided,
-            the default expansion function simply expands all operations that
-            have ``Operation.grad_method=None`` until all resulting operations
-            have a defined gradient method.
-        differentiable (bool): Specifies whether the gradient transform is differentiable or
-            not. A transform may be non-differentiable if it does not use an
-            autodiff framework for its tensor manipulations. In such a case, setting
-            ``differentiable=False`` instructs the decorator
-            to mark the output as 'constant', reducing potential overhead.
-        hybrid (bool): Specifies whether classical processing inside a QNode
-            should be taken into account when transforming a QNode.
-
-            - If ``True``, and classical processing is detected and this
-              option is set to ``True``, the Jacobian of the classical
-              processing will be computed and included. When evaluated, the
-              returned Jacobian will be with respect to the QNode arguments.
-
-            - If ``False``, any internal QNode classical processing will be
-              **ignored**. When evaluated, the returned Jacobian will be with
-              respect to the **gate** arguments, and not the QNode arguments.
-
-    Supported gradient transforms must be of the following form:
-
-    .. code-block:: python
-
-        @gradient_transform
-        def my_custom_gradient(tape, argnum=None, **kwargs):
-            ...
-            return gradient_tapes, processing_fn
-
-    where:
-
-    - ``tape`` (*QuantumTape*): the input quantum tape to compute the gradient of
-
-    - ``argnum`` (*int* or *list[int]* or *None*): Which trainable parameters of the tape
-      to differentiate with respect to. If not provided, the derivatives with respect to all
-      trainable inputs of the tape should be returned (``tape.trainable_params``).
-
-    - ``gradient_tapes`` (*list[QuantumTape]*): is a list of output tapes to be evaluated.
-      If this list is empty, no quantum evaluations will be made.
-
-    - ``processing_fn`` is a processing function to be applied to the output of the evaluated
-      ``gradient_tapes``. It should accept a list of numeric results with length ``len(gradient_tapes)``,
-      and return the Jacobian matrix.
-
-    Once defined, the quantum gradient transform can be used as follows:
-
-    >>> gradient_tapes, processing_fn = my_custom_gradient(tape, *gradient_kwargs)
-    >>> res = execute(tapes, dev, interface="autograd", gradient_fn=qml.gradients.param_shift)
-    >>> jacobian = processing_fn(res)
-
-    Alternatively, gradient transforms can be applied directly to QNodes,
-    in which case the execution is implicit:
-
-    >>> fn = my_custom_gradient(qnode, *gradient_kwargs)
-    >>> fn(weights) # transformed function takes the same arguments as the QNode
-    1.2629730888100839
-
-    .. note::
-
-        The input tape might have parameters of various types, including
-        NumPy arrays, JAX Arrays, and TensorFlow and PyTorch tensors.
-
-        If the gradient transform is written in a autodiff-compatible manner, either by
-        using a framework such as Autograd or TensorFlow, or by using ``qml.math`` for
-        tensor manipulation, then higher-order derivatives will also be supported.
-
-        Alternatively, you may use the ``tape.unwrap()`` context manager to temporarily
-        convert all tape parameters to NumPy arrays and floats:
-
-        >>> with tape.unwrap():
-        ...     params = tape.get_parameters()  # list of floats
-    """
-
-    def __repr__(self):
-        return f"<gradient_transform: {self.__name__}>"  # pylint: disable=no-member
-
-    def __init__(
-        self, transform_fn, expand_fn=expand_invalid_trainable, differentiable=True, hybrid=True
-    ):
-        self.hybrid = hybrid
-        super().__init__(transform_fn, expand_fn=expand_fn, differentiable=differentiable)
-
-    def default_qnode_wrapper(self, qnode, targs, tkwargs):  # pylint: disable=too-many-statements
-        # Here, we overwrite the QNode execution wrapper in order
-        # to take into account that classical processing may be present
-        # inside the QNode.
-        hybrid = tkwargs.pop("hybrid", self.hybrid)
-        _wrapper = super().default_qnode_wrapper(qnode, targs, tkwargs)
-
-        def jacobian_wrapper(
-            *args, **kwargs
-        ):  # pylint: disable=too-many-return-statements, too-many-branches, too-many-statements
-            argnums = tkwargs.get("argnums", None)
-
-            interface = qml.math.get_interface(*args)
-            trainable_params = qml.math.get_trainable_indices(args)
-
-            if interface == "jax" and tkwargs.get("argnum", None):
-                raise qml.QuantumFunctionError(
-                    "argnum does not work with the Jax interface. You should use argnums instead."
-                )
-
-            if interface == "jax" and not trainable_params:
-                if argnums is None:
-                    argnums_ = [0]
-
-                else:
-                    argnums_ = [argnums] if isinstance(argnums, int) else argnums
-
-                params = qml.math.jax_argnums_to_tape_trainable(
-                    qnode, argnums_, self.expand_fn, args, kwargs
-                )
-                argnums_ = qml.math.get_trainable_indices(params)
-                kwargs["argnums"] = argnums_
-
-            elif not trainable_params:
-                warnings.warn(
-                    "Attempted to compute the gradient of a QNode with no trainable parameters. "
-                    "If this is unintended, please add trainable parameters in accordance with "
-                    "the chosen auto differentiation framework."
-                )
-                return ()
-
-            qjac = _wrapper(*args, **kwargs)
-
-            if not hybrid:
-                return qjac
-
-            kwargs.pop("shots", False)
-
-            # Special case where we apply a Jax transform (jacobian e.g.) on the gradient transform and argnums are
-            # defined on the outer transform and therefore on the args.
-            argnum_cjac = trainable_params or argnums if interface == "jax" else None
-            cjac = qml.gradients.classical_jacobian(
-                qnode, argnum=argnum_cjac, expand_fn=self.expand_fn
-            )(*args, **kwargs)
-
-            return _contract_qjac_with_cjac(qjac, cjac, qnode.tape)  # pragma: no cover
-
-        return jacobian_wrapper