Update session.from_id()

qiskit_ibm_runtime/session.py

@@ -23,6 +23,8 @@
 from .runtime_program import ParameterNamespace
 from .program.result_decoder import ResultDecoder
 from .ibm_backend import IBMBackend
+from .exceptions import IBMInputValueError
+from .utils.deprecation import deprecate_arguments
 from .utils.default_session import set_cm_session
 
 
@@ -282,25 +284,44 @@ def service(self) -> QiskitRuntimeService:
     def from_id(
         cls,
         session_id: str,
-        service: Optional[QiskitRuntimeService] = None,
+        service: QiskitRuntimeService,
         backend: Optional[Union[str, IBMBackend]] = None,
     ) -> "Session":
         """Construct a Session object with a given session_id
 
         Args:
-            session_id: the id of the session to be created. This can be an already
+            session_id: the id of the session to be created. This must be an already
                 existing session id.
             service: instance of the ``QiskitRuntimeService`` class.
             backend: instance of :class:`qiskit_ibm_runtime.IBMBackend` class or
                 string name of backend.
 
+        Raises:
+            IBMInputValueError: If given `session_id` does not exist. or the backend passed in does
+                not match the original session backend.
+
         Returns:
             A new Session with the given ``session_id``
-
         """
-        session = cls(service, backend)
-        session._session_id = session_id
-        return session
+
+        if backend:
+            deprecate_arguments("backend", "0.15.0", "Sessions do not support multiple backends.")
+            if isinstance(backend, IBMBackend):
+                backend = backend.name
+
+        response = service._api_client.session_details(session_id)
+        if response:
+            session_backend = response.get("backend_name")
+            if backend and backend != session_backend:
+                raise IBMInputValueError(
+                    f"The session_id {session_id} was created with backend {session_backend}, "
+                    f"but backend {backend} was given."
+                )
+            session = cls(service, session_backend)
+            session._session_id = session_id
+            return session
+
+        raise IBMInputValueError(f"The session_id {session_id} does not exist.")
 
     def __enter__(self) -> "Session":
         set_cm_session(self)

releasenotes/notes/from-id-params-659a2adb727b9d18.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    The ``backend`` parameter in :meth:`~qiskit_ibm_runtime.Session.from_id` is being deprecated because
+    sessions do not support multiple backends. Additionally, the `service` parameter is no longer optional.
+

test/integration/test_session.py

@@ -21,6 +21,7 @@
 from qiskit.result import Result
 
 from qiskit_ibm_runtime import Estimator, Session, Sampler, Options
+from qiskit_ibm_runtime.exceptions import IBMInputValueError
 
 from ..decorators import run_integration_test, quantum_only
 from ..ibm_test_case import IBMIntegrationTestCase
@@ -90,16 +91,16 @@ def test_using_correct_instance(self, service):
 
     @run_integration_test
     def test_session_from_id(self, service):
-        """Test creating a session from a given id"""
+        """Test creating a session with from_id with simulator."""
         backend = service.backend("ibmq_qasm_simulator")
-        with Session(service, backend=backend) as session:
-            sampler = Sampler(session=session)
-            job = sampler.run(ReferenceCircuits.bell(), shots=400)
-            session_id = job.session_id
-        new_session = Session.from_id(backend=backend, session_id=session_id)
-        sampler = Sampler(session=new_session)
+        session = Session(service=service, backend=backend)
+
+        sampler = Sampler(session=session)
         job = sampler.run(ReferenceCircuits.bell(), shots=400)
-        self.assertEqual(session_id, job.session_id)
+        session_id = job.session_id
+
+        with self.assertRaises(IBMInputValueError):
+            _ = Session.from_id(session_id=session_id, service=service)
 
 
 class TestBackendRunInSession(IBMIntegrationTestCase):