Fix premature session closure error

CHANGELOG.md

@@ -13,13 +13,16 @@
 
 ### Documentation 📝
 
-### Bug fixes 🐛
+### Bug fixes 🐛  
+* Fixed premature session closure when using `qiskit_session`.  
+  [(#608)](https://github.com/PennyLaneAI/pennylane-qiskit/pull/608)
 
 ### Contributors ✍️
 
 This release contains contributions from (in alphabetical order):
 
 Andrija Paurevic
+Tak Hur
 
 ---
 # Release 0.39.1

pennylane_qiskit/converter.py

@@ -573,7 +573,6 @@ def _function(*args, params: dict = None, wires: list = None, **kwargs):
                         mid_circ_regs[carg] = mid_circ_meas[-1]
 
             else:
-
                 try:
                     if not isinstance(instruction, (ControlFlowOp,)):
                         operation_args = [instruction.to_matrix()]

pennylane_qiskit/qiskit_device.py

@@ -15,7 +15,7 @@
 This module contains a prototype base class for constructing Qiskit devices
 for PennyLane with the new device API.
 """
-# pylint: disable=too-many-instance-attributes,attribute-defined-outside-init
+# pylint: disable=too-many-instance-attributes,attribute-defined-outside-init,too-many-positional-arguments
 
 
 import warnings
@@ -325,7 +325,6 @@ def __init__(
         compile_backend=None,
         **kwargs,
     ):
-
         if shots is None:
             warnings.warn(
                 "Expected an integer number of shots, but received shots=None. Defaulting "
@@ -592,7 +591,8 @@ def execute_circuits(session):
                     results.append(execute_fn(circ, session))
                 yield results
             finally:
-                session.close()
+                if self._session is None:
+                    session.close()
 
         with execute_circuits(session) as results:
             return results

pennylane_qiskit/qiskit_device_legacy.py

@@ -105,7 +105,6 @@
     _eigs = {}
 
     def __init__(self, wires, provider, backend, shots=1024, **kwargs):
-
         super().__init__(wires=wires, shots=shots)
 
         self.provider = provider
@@ -379,7 +378,7 @@
             state = unitary @ initial_state
 
         # reverse qubit order to match PennyLane convention
         return state.reshape([2] * self.num_wires).T.flatten()
 
     def generate_samples(self, circuit=None):
         r"""Returns the computational basis samples generated for all wires.