Use lazy-importing of qnn module and remove Python 3.6 (#1228)

* Revert "Add deprecation warning to qnn module (#1170)" This reverts commit 816885a. * Remove Python 3.6 and add 3.9 * Add lazy loading * Add tests * Add to changelog * Mention 3.9 * Update CI * Add to docs * Fix * Fix note * Allow importing of module * Change order * Change back * Update test * Fix * full stop * black * Apply suggestions from code review Co-authored-by: Tom Bromley <49409390+trbromley@users.noreply.github.com> Co-authored-by: Josh Izaac <josh146@gmail.com>
PennyLaneAI · May 6, 2021 · 9f01932 · 9f01932
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diff --git a/.github/CHANGELOG.md b/.github/CHANGELOG.md
@@ -117,6 +117,9 @@ random_mat2 = rng.standard_normal(3, requires_grad=False)
 
 <h3>Breaking changes</h3>
 
+* Removes support for Python 3.6 and begin testing for Python 3.9.
+  [(#1228)](https://github.com/XanaduAI/pennylane/pull/1228)
+
 <h3>Bug fixes</h3>
 
 <h3>Documentation</h3>

diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
@@ -19,10 +19,10 @@ jobs:
     strategy:
       matrix:
         config:
-          - {python-version: 3.6, interfaces: ['tf']}
+          - {python-version: 3.7, interfaces: ['tf']}
           - {python-version: 3.7, interfaces: ['torch']}
           - {python-version: 3.8, interfaces: ['tf', 'torch', 'jax']}
-          - {python-version: 3.8, interfaces: []}
+          - {python-version: 3.9, interfaces: []}
 
     steps:
       - name: Cancel Previous Runs

diff --git a/.readthedocs.yml b/.readthedocs.yml
@@ -19,7 +19,7 @@ formats:
 
 # Optionally set the version of Python and requirements required to build your docs
 python:
-  version: 3.6
+  version: 3.8
   install:
     - requirements: doc/requirements.txt
     - requirements: qchem/requirements.txt

diff --git a/README.md b/README.md
@@ -61,7 +61,7 @@
 
 ## Installation
 
-PennyLane requires Python version 3.6 and above. Installation of PennyLane, as well as all
+PennyLane requires Python version 3.7 and above. Installation of PennyLane, as well as all
 dependencies, can be done using pip:
 
 ```console

diff --git a/doc/_templates/autosummary/class_no_inherited.rst b/doc/_templates/autosummary/class_no_inherited.rst
@@ -0,0 +1,90 @@
+{{ fullname | replace("pennylane", "qml") }}
+{{ underline }}
+
+.. autoclass:: {{ fullname }}
+   :show-inheritance:
+
+   {% if '__init__' in methods %}
+     {% set caught_result = methods.remove('__init__') %}
+   {% endif %}
+
+   {% block attributes_documentation %}
+   {% if attributes %}
+
+   .. raw:: html
+
+      <a class="attr-details-header collapse-header" data-toggle="collapse" href="#attrDetails" aria-expanded="false" aria-controls="attrDetails">
+         <h2 style="font-size: 24px;">
+            <i class="fas fa-angle-down rotate" style="float: right;"></i> Attributes
+         </h2>
+      </a>
+      <div class="collapse" id="attrDetails">
+
+   {% block attributes_summary %}
+   {% if attributes %}
+
+   .. autosummary::
+      :nosignatures:
+   {% for item in attributes %}
+      ~{{ name }}.{{ item }}
+   {%- endfor %}
+
+   {% endif %}
+   {% endblock %}
+
+   {% for item in attributes %}
+   {%- if item not in inherited_members %}
+   .. autoattribute:: {{ item }}
+   {%- endif %}
+   {%- endfor %}
+
+   .. raw:: html
+
+      </div>
+
+   {% endif %}
+   {% endblock %}
+
+   {% block methods_documentation %}
+   {% if methods %}
+
+   .. raw:: html
+
+      <a class="meth-details-header collapse-header" data-toggle="collapse" href="#methDetails" aria-expanded="false" aria-controls="methDetails">
+         <h2 style="font-size: 24px;">
+            <i class="fas fa-angle-down rotate" style="float: right;"></i> Methods
+         </h2>
+      </a>
+      <div class="collapse" id="methDetails">
+
+   {% block methods_summary %}
+   {% if methods %}
+
+   .. autosummary::
+   {% for item in methods %}
+      ~{{ name }}.{{ item }}
+   {%- endfor %}
+
+   {% endif %}
+   {% endblock %}
+
+   {% for item in methods %}
+   {%- if item not in inherited_members %}
+   .. automethod:: {{ item }}
+   {%- endif %}
+   {%- endfor %}
+
+   .. raw:: html
+
+      </div>
+
+   {% endif %}
+   {% endblock %}
+
+   .. raw:: html
+
+      <script type="text/javascript">
+         $(".collapse-header").click(function () {
+             $(this).children('h2').eq(0).children('i').eq(0).toggleClass("up");
+         })
+      </script>
diff --git a/doc/code/qml_qnn.rst b/doc/code/qml_qnn.rst
@@ -3,7 +3,4 @@ qml.qnn
 
 .. currentmodule:: pennylane.qnn
 
-.. automodapi:: pennylane.qnn
-    :no-heading:
-    :no-inheritance-diagram:
-    :no-inherited-members:
+.. automodule:: pennylane.qnn
diff --git a/doc/development/guide/installation.rst b/doc/development/guide/installation.rst
@@ -6,7 +6,7 @@ Dependencies
 
 PennyLane requires the following libraries be installed:
 
-* `Python <http://python.org/>`_ >= 3.6
+* `Python <http://python.org/>`_ >= 3.7
 
 as well as the following Python packages:
 

diff --git a/pennylane/qnn/__init__.py b/pennylane/qnn/__init__.py
@@ -11,9 +11,40 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-"""This module contains classes and functions for constructing quantum neural networks from QNodes."""
+"""
+This module contains functionality for converting PennyLane QNodes into layers that are compatible
+with Keras and PyTorch.
 
-import pennylane.qnn.cost
+.. note::
 
-from .keras import KerasLayer
-from .torch import TorchLayer
+    Check out our :doc:`Keras <demos/tutorial_qnn_module_tf>` and
+    :doc:`Torch <demos/tutorial_qnn_module_torch>` tutorials for further details.
+
+
+.. rubric:: Classes
+
+.. autosummary::
+    :toctree: api
+    :nosignatures:
+    :template: autosummary/class_no_inherited.rst
+
+    ~KerasLayer
+    ~TorchLayer
+"""
+import importlib
+
+from . import cost
+
+class_map = {"KerasLayer": "keras", "TorchLayer": "torch"}
+mods = ("keras", "torch")
+
+
+def __getattr__(name):
+    """Allow for lazy-loading of KerasLayer and TorchLayer so that TensorFlow and PyTorch are not
+    automatically loaded with PennyLane"""
+    if name in class_map:
+        mod = importlib.import_module("." + class_map[name], __name__)
+        return getattr(mod, name)
+    if name in mods:
+        return importlib.import_module("." + name, __name__)
+    raise AttributeError(f"module {__name__!r} has no attribute {name!r}")
diff --git a/pennylane/qnn/keras.py b/pennylane/qnn/keras.py
@@ -32,7 +32,8 @@
 
 
 class KerasLayer(Layer):
-    """Converts a :func:`~.QNode` to a Keras
+    """KerasLayer(qnode, weight_shapes: dict, output_dim, weight_specs: Optional[dict] = None, **kwargs)
+    Converts a :func:`~.QNode` to a Keras
     `Layer <https://www.tensorflow.org/api_docs/python/tf/keras/layers/Layer>`__.
 
     The result can be used within the Keras
@@ -49,7 +50,7 @@ class KerasLayer(Layer):
             specifications for weights used in the QNode, such as the method of parameter
             initialization. This specification is provided as a dictionary with keys given by the
             arguments of the `add_weight()
-            <https://www.tensorflow.org/api_docs/python/tf/keras/layers/Layer#add_weight>`__.
+            <https://www.tensorflow.org/api_docs/python/tf/keras/layers/Layer#add_weight>`__
             method and values being the corresponding specification.
         **kwargs: additional keyword arguments passed to the Layer_ base class
 

diff --git a/qchem/setup.py b/qchem/setup.py
@@ -51,9 +51,9 @@
     "Operating System :: Microsoft :: Windows",
     "Programming Language :: Python",
     "Programming Language :: Python :: 3",
-    "Programming Language :: Python :: 3.6",
     "Programming Language :: Python :: 3.7",
     "Programming Language :: Python :: 3.8",
+    "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3 :: Only",
     "Topic :: Scientific/Engineering :: Physics",
 ]

diff --git a/setup.py b/setup.py
@@ -73,9 +73,9 @@
     "Operating System :: Microsoft :: Windows",
     "Programming Language :: Python",
     'Programming Language :: Python :: 3',
-    'Programming Language :: Python :: 3.6',
     'Programming Language :: Python :: 3.7',
     'Programming Language :: Python :: 3.8',
+    'Programming Language :: Python :: 3.9',
     'Programming Language :: Python :: 3 :: Only',
     "Topic :: Scientific/Engineering :: Physics"
 ]

diff --git a/tests/qnn/test_keras.py b/tests/qnn/test_keras.py
@@ -18,7 +18,8 @@
 import pytest
 
 import pennylane as qml
-from pennylane.qnn.keras import KerasLayer
+
+KerasLayer = qml.qnn.keras.KerasLayer
 
 tf = pytest.importorskip("tensorflow", minversion="2")
 
@@ -609,3 +610,9 @@ def test_model_save_weights_dm(self, model_dm, n_qubits, tmpdir):
         assert np.allclose(prediction, prediction_loaded)
         for i, w in enumerate(weights):
             assert np.allclose(w, weights_loaded[i])
+
+
+def test_no_attribute():
+    """Test that the qnn module raises an AttributeError if accessing an unavailable attribute"""
+    with pytest.raises(AttributeError, match="module 'pennylane.qnn' has no attribute 'random'"):
+        qml.qnn.random