Removed old return type (#331)

* Removed old return

* Fixed tests; changelog

* Added link to changelog

* Trigger CI

* Codefactor

* Additional changes

CHANGELOG.md

@@ -6,6 +6,9 @@
 
 ### Breaking changes 💔
 
+* The old return type system has been removed.
+  [(#331)](https://github.com/PennyLaneAI/pennylane-qiskit/pull/331)
+
 ### Deprecations 👋
 
 ### Documentation 📝
@@ -16,6 +19,8 @@
 
 This release contains contributions from (in alphabetical order):
 
+Mudit Pandey,
+
 ---
 # Release 0.32.0
 

pennylane_qiskit/qiskit_device.py

@@ -22,7 +22,6 @@
 import warnings
 
 import numpy as np
-import pennylane
 from qiskit import ClassicalRegister, QuantumCircuit, QuantumRegister
 from qiskit import extensions as ex
 from qiskit.compiler import transpile
@@ -499,15 +498,10 @@ def batch_execute(self, circuits, timeout: int = None):
             if self.shots is not None or circuit.is_sampled:
                 self._samples = self.generate_samples(circuit_obj)
 
-            if not pennylane.active_return():
-                res = self._statistics_legacy(circuit)
-                res = np.asarray(res)
-                results.append(res)
-            else:
-                res = self.statistics(circuit)
-                single_measurement = len(circuit.measurements) == 1
-                res = res[0] if single_measurement else tuple(res)
-                results.append(res)
+            res = self.statistics(circuit)
+            single_measurement = len(circuit.measurements) == 1
+            res = res[0] if single_measurement else tuple(res)
+            results.append(res)
 
         if self.tracker.active:
             self.tracker.update(batches=1, batch_len=len(circuits))

tests/test_qiskit_device.py

@@ -140,31 +140,6 @@ def test_calls_to_reset(self, n_tapes, mocker, device):
 
         assert spy.call_count == n_tapes
 
-    def test_result_legacy(self, device, tol):
-        """Tests that the result has the correct shape and entry types."""
-        # TODO: remove once the legacy return system is removed.
-        qml.disable_return()
-        dev = device(2)
-        tapes = [self.tape1, self.tape2]
-        res = dev.batch_execute(tapes)
-
-        # We're calling device methods directly, need to reset before the next
-        # execution
-        dev.reset()
-        tape1_expected = dev.execute(self.tape1)
-
-        dev.reset()
-        tape2_expected = dev.execute(self.tape2)
-
-        assert len(res) == 2
-        assert isinstance(res[0], np.ndarray)
-        assert np.allclose(res[0], tape1_expected, atol=0)
-
-        assert isinstance(res[1], np.ndarray)
-        assert np.allclose(res[1], tape2_expected, atol=0)
-
-        qml.enable_return()
-
     def test_result(self, device, tol):
         """Tests that the result has the correct shape and entry types."""
         dev = device(2)