Optional new pennylane functionality

Author: mpharrigan

qualtran/_infra/bloq.py

@@ -484,7 +484,13 @@ def as_pl_op(self, wires: 'Wires') -> 'Operation':
                 instance truly should not be included in the PennyLane circuit (e.g. for reshaping
                 bloqs). A bloq with no PennyLane equivalent should raise an exception instead.
         """
-        from pennylane.io import FromBloq
+        try:
+            from pennylane.io import FromBloq
+        except ImportError:
+            raise NotImplementedError(
+                f"{self} does not have a native PennyLane operation. "
+                f"pennylane>=0.41 will wrap this bloq in the `pennylane.io.FromBloq` adapter."
+            )
 
         return FromBloq(bloq=self, wires=wires)
 

qualtran/_infra/bloq_test.py

@@ -37,6 +37,9 @@ def test_bloq():
 def test_as_pl_op():
     import pennylane as qml
 
+    if not hasattr(qml, 'FromBloq'):
+        pytest.xfail("Requires pennylane>=0.41")
+
     tb = TestTwoBitOp()
 
     assert tb.as_pl_op(wires=[0, 1]) == qml.FromBloq(TestTwoBitOp(), wires=[0, 1])

qualtran/bloqs/basic_gates/cnot_test.py

@@ -42,6 +42,8 @@ def test_cnot_tensor():
 
 def test_cnot_vs_pl():
     bloq = CNOT()
+    if not hasattr(qml, 'FromBloq'):
+        pytest.xfail("requires pennylane>=0.41")
     matrix = qml.FromBloq(bloq, wires=[0, 1]).matrix()
     # fmt: off
     should_be = np.array([