Remove old return type, mode kwarg (#4503)

* remove old return type * Changelog * Remove numpy unpinning * Update * Update * More tests * Apply suggestions from code review Co-authored-by: Mudit Pandey <mudit.pandey@xanadu.ai> * Update doc/development/deprecations.rst Co-authored-by: Mudit Pandey <mudit.pandey@xanadu.ai> * Remove unused function * Remove a lot of imports * Linting * More update * Comments * Remove qscript shape * Remove unused import * Remove compute vjp * Remove test * Remove compute_vjp in torch * Remove from doc compute vjp * Remove pylint * Hessian coverage * Unused import --------- Co-authored-by: Mudit Pandey <mudit.pandey@xanadu.ai>
PennyLaneAI · Aug 24, 2023 · 6b71579 · 6b71579
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diff --git a/.github/workflows/interface-unit-tests.yml b/.github/workflows/interface-unit-tests.yml
@@ -46,7 +46,7 @@ jobs:
       pytorch_version: ${{ inputs.pytorch_version }}
       install_pennylane_lightning_master: true
       pytest_coverage_flags: ${{ inputs.pytest_coverage_flags }}
-      pytest_markers: torch and not qcut and not legacy and not finite-diff and not param-shift
+      pytest_markers: torch and not qcut and not finite-diff and not param-shift
 
 
   autograd-tests:
@@ -67,7 +67,7 @@ jobs:
       install_pytorch: false
       install_pennylane_lightning_master: true
       pytest_coverage_flags: ${{ inputs.pytest_coverage_flags }}
-      pytest_markers: autograd and not qcut and not legacy and not finite-diff and not param-shift
+      pytest_markers: autograd and not qcut and not finite-diff and not param-shift
 
 
   tf-tests:
@@ -92,7 +92,7 @@ jobs:
       install_pytorch: false
       install_pennylane_lightning_master: true
       pytest_coverage_flags: ${{ inputs.pytest_coverage_flags }}
-      pytest_markers: tf and not qcut and not legacy and not finite-diff and not param-shift
+      pytest_markers: tf and not qcut and not finite-diff and not param-shift
       pytest_additional_args: --splits 2 --group ${{ matrix.group }}
       additional_pip_packages: pytest-split
 
@@ -118,7 +118,7 @@ jobs:
       install_pytorch: false
       install_pennylane_lightning_master: true
       pytest_coverage_flags: ${{ inputs.pytest_coverage_flags }}
-      pytest_markers: jax and not qcut and not legacy and not finite-diff and not param-shift
+      pytest_markers: jax and not qcut and not finite-diff and not param-shift
       pytest_additional_args: --splits 2 --group ${{ matrix.group }}
       additional_pip_packages: pytest-split
 
@@ -144,7 +144,7 @@ jobs:
       install_pytorch: false
       install_pennylane_lightning_master: true
       pytest_coverage_flags: ${{ inputs.pytest_coverage_flags }}
-      pytest_markers: core and not qcut and not legacy and not finite-diff and not param-shift
+      pytest_markers: core and not qcut and not finite-diff and not param-shift
       pytest_additional_args: --splits 2 --group ${{ matrix.group }}
       additional_pip_packages: pytest-split
 
@@ -219,26 +219,6 @@ jobs:
       pytest_markers: qchem
       additional_pip_packages: openfermionpyscf basis-set-exchange
 
-
-  legacy-tests:
-    uses: ./.github/workflows/unit-test.yml
-    with:
-      job_name: legacy-tests
-      branch: ${{ inputs.branch }}
-      coverage_artifact_name: legacy-coverage
-      python_version: 3.9
-      install_jax: true
-      jax_version: ${{ inputs.jax_version }}
-      install_tensorflow: true
-      tensorflow_version: ${{ inputs.tensorflow_version }}
-      keras_version: ${{ inputs.tensorflow_version }}
-      install_pytorch: true
-      pytorch_version: ${{ inputs.pytorch_version }}
-      install_pennylane_lightning_master: false
-      pytest_coverage_flags: ${{ inputs.pytest_coverage_flags }}
-      pytest_markers: legacy
-
-
   gradients-tests:
     strategy:
       matrix:
@@ -325,7 +305,6 @@ jobs:
       - zx-tests
       - qcut-tests
       - qchem-tests
-      - legacy-tests
       - gradients-tests
       - data-tests
       - device-tests

diff --git a/doc/development/deprecations.rst b/doc/development/deprecations.rst
@@ -12,18 +12,6 @@ Pending deprecations
   - Deprecated in v0.32
   - Removed in v0.33
 
-* ``qml.enable_return`` and ``qml.disable_return`` are deprecated. Please avoid calling
-  ``disable_return``, as the old return system is deprecated along with these switch functions.
-
-  - Deprecated in v0.32
-  - Will be removed in v0.33
-
-* The ``mode`` keyword argument in ``QNode`` is deprecated, as it was only used in the old return
-  system (which is also deprecated). Please use ``grad_on_execution`` instead.
-
-  - Deprecated in v0.32
-  - Will be removed in v0.33
-
 * The ``observables`` argument in ``QubitDevice.statistics`` is deprecated. Please use ``circuit``
   instead. Using a list of observables in ``QubitDevice.statistics`` is deprecated. Please use a
   ``QuantumTape`` instead.
@@ -147,6 +135,17 @@ Pending deprecations
 Completed deprecation cycles
 ----------------------------
 
+* ``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.

diff --git a/doc/introduction/returns.rst b/doc/introduction/returns.rst
@@ -115,12 +115,21 @@ select the option below that describes your situation.
           x = np.array(0.5, requires_grad=True)
           qml.jacobian(circuit)(x)
 
-      Follow the instructions :ref:`here <return-autograd-tf-gotcha>` to fix this issue, which
-      arises because NumPy and TensorFlow do not support differentiating tuples.
-      Alternatively, consider porting your code to use the :ref:`JAX <jax_interf>` or
+
+      Use stacking to fix this issue (see below), which arises because NumPy and TensorFlow do not support
+      differentiating tuples. Alternatively, consider porting your code to use the :ref:`JAX <jax_interf>` or
       :ref:`Torch <torch_interf>` interface, which could unlock additional features and performance
       benefits!
 
+    .. code-block:: python
+
+            with tf.GradientTape() as tape:
+                res = circuit(a, b)
+                res = tf.stack(res)
+
+            x = np.array(0.5, requires_grad=True)
+            qml.jacobian(circuit)(x)
+
     * You are returning differently-shaped quantities together, such as
       :func:`expval() <pennylane.expval>` and :func:`probs() <pennylane.probs>`. For example, the
       following code is compatible with version 0.29 of PennyLane but will raise an error in version
@@ -183,7 +192,3 @@ select the option below that describes your situation.
     - If you suspect that your issue is due to a bug in PennyLane itself, please open a
       `bug report <https://github.com/PennyLaneAI/pennylane/issues/new?labels=bug+%3Abug%3A&template=bug_report.yml&title=[BUG]>`_
       on the PennyLane GitHub page.
-
-    - As a *last resort*, you can place :func:`qml.disable_return() <.disable_return>` at the top of
-      your code. This will revert PennyLane's behaviour to the QNode return type in version 0.29.
-      However, be aware that this capability will be removed in a future version of PennyLane!
diff --git a/doc/releases/changelog-dev.md b/doc/releases/changelog-dev.md
@@ -8,6 +8,12 @@
 
 <h3>Breaking changes 💔</h3>
 
+* The old return type and associated functions ``qml.enable_return`` and ``qml.disable_return`` are removed.
+ [#4503](https://github.com/PennyLaneAI/pennylane/pull/4503)
+
+* The ``mode`` keyword argument in ``QNode`` is removed. Please use ``grad_on_execution`` instead.
+ [#4503](https://github.com/PennyLaneAI/pennylane/pull/4503)
+
 <h3>Deprecations 👋</h3>
 
 <h3>Documentation 📝</h3>
@@ -16,4 +22,6 @@
 
 <h3>Contributors ✍️</h3>
 
-This release contains contributions from (in alphabetical order):
+This release contains contributions from (in alphabetical order):
+
+Romain Moyard
diff --git a/pennylane/__init__.py b/pennylane/__init__.py
@@ -83,7 +83,6 @@
 from pennylane.templates.subroutines import *
 from pennylane import qaoa
 from pennylane.qnode import QNode, qnode
-from pennylane.return_types import enable_return, disable_return, active_return
 from pennylane.transforms import (
     adjoint_metric_tensor,
     batch_params,

diff --git a/pennylane/_grad.py b/pennylane/_grad.py
@@ -22,8 +22,6 @@
 from autograd.extend import vspace
 from autograd.wrap_util import unary_to_nary
 
-from pennylane.return_types import active_return
-
 make_vjp = unary_to_nary(_make_vjp)
 
 
@@ -329,18 +327,8 @@ def _jacobian_function(*args, **kwargs):
                 "If this is unintended, please add trainable parameters via the "
                 "'requires_grad' attribute or 'argnum' keyword."
             )
-        try:
-            jac = tuple(_jacobian(func, arg)(*args, **kwargs) for arg in _argnum)
-        except TypeError as e:
-            if active_return():
-                raise ValueError(
-                    "PennyLane has a new return shape specification that"
-                    " may not work well with autograd and more than one measurement. That may"
-                    " be the source of the error. \n\n"
-                    "See the documentation here for more information:\n"
-                    "https://docs.pennylane.ai/en/stable/introduction/returns.html"
-                ) from e
-            raise e
+
+        jac = tuple(_jacobian(func, arg)(*args, **kwargs) for arg in _argnum)
 
         return jac[0] if unpack else jac