Use service defined by user as default (#955)

* Adding global service

* Added tests for global service

* Fixed failing tests

* black

* Syntax changes

* Restored test

* Fixed tests that were failing. mock_service.global_service must be initialized for it to work correctly

* Fixed test and added another case to a test

* Fix in test

* Release note

---------

Co-authored-by: Kevin Tian <[email protected]>

qiskit_ibm_runtime/base_primitive.py

@@ -105,7 +105,11 @@ def __init__(
                 version="0.10.0",
                 remedy="Please pass it as the ``backend`` parameter instead.",
             )
-            self._service = QiskitRuntimeService()
+            self._service = (
+                QiskitRuntimeService()
+                if QiskitRuntimeService.global_service is None
+                else QiskitRuntimeService.global_service
+            )
             self._backend = self._service.backend(session)
         elif isinstance(backend, Session):
             issue_deprecation_msg(
@@ -123,7 +127,11 @@ def __init__(
             self._service = backend.service
             self._backend = backend
         elif isinstance(backend, str):
-            self._service = QiskitRuntimeService()
+            self._service = (
+                QiskitRuntimeService()
+                if QiskitRuntimeService.global_service is None
+                else QiskitRuntimeService.global_service
+            )
             self._backend = self._service.backend(backend)
         elif get_cm_session():
             self._session = get_cm_session()
@@ -132,7 +140,11 @@ def __init__(
                 name=self._session.backend(), instance=self._session._instance
             )
         else:
-            self._service = QiskitRuntimeService()
+            self._service = (
+                QiskitRuntimeService()
+                if QiskitRuntimeService.global_service is None
+                else QiskitRuntimeService.global_service
+            )
             if self._service.channel != "ibm_cloud":
                 raise ValueError(
                     "A backend or session must be specified when not using ibm_cloud channel."

qiskit_ibm_runtime/qiskit_runtime_service.py

@@ -118,6 +118,8 @@ class QiskitRuntimeService(Provider):
     canceling job.
     """
 
+    global_service = None
+
     def __init__(
         self,
         channel: Optional[ChannelType] = None,
@@ -199,6 +201,7 @@ def __init__(
             self._api_client = RuntimeClient(self._client_params)
             # TODO: We can make the backend discovery lazy
             self._backends = self._discover_cloud_backends()
+            QiskitRuntimeService.global_service = self
             return
         else:
             auth_client = self._authenticate_ibm_quantum_account(self._client_params)
@@ -211,6 +214,7 @@ def __init__(
                 for backend_name in hgp.backends:
                     if backend_name not in self._backends:
                         self._backends[backend_name] = None
+        QiskitRuntimeService.global_service = self
 
         # TODO - it'd be nice to allow some kind of autocomplete, but `service.ibmq_foo`
         # just seems wrong since backends are not runtime service instances.

qiskit_ibm_runtime/session.py

@@ -99,9 +99,15 @@ def __init__(
         """
 
         if service is None:
-            self._service = (
-                backend.service if isinstance(backend, IBMBackend) else QiskitRuntimeService()
-            )
+            if isinstance(backend, IBMBackend):
+                self._service = backend.service
+            else:
+                self._service = (
+                    QiskitRuntimeService()
+                    if QiskitRuntimeService.global_service is None
+                    else QiskitRuntimeService.global_service
+                )
+
         else:
             self._service = service
 

releasenotes/notes/global_service-ad56a0209e7b9891.yaml

@@ -0,0 +1,11 @@
+---
+features:
+  - |
+    Added a ``global_service``, so that if the user defines a `QiskitRuntimeService`, it will
+    be used by the primitives, even if the service is not passed to them explicitly.
+    For example::
+    
+      from qiskit_ibm_runtime import QiskitRuntimeService, Sampler
+      service = QiskitRuntimeService(channel="ibm_quantum")
+      # Sampler._service field will be initialized to ``service``
+      sampler = Sampler(backend="ibmq_qasm_simulator")

test/unit/test_ibm_primitives.py

@@ -155,6 +155,7 @@ def test_init_with_backend_str(self):
                 mock_service.return_value = mock_service_inst
                 mock_backend = MagicMock()
                 mock_backend.name = backend_name
+                mock_service.global_service = None
                 mock_service_inst.backend.return_value = mock_backend
 
                 inst = cls(backend=backend_name)
@@ -176,6 +177,7 @@ def test_init_with_session_backend_str(self):
             ) as mock_service:
                 with self.assertWarns(DeprecationWarning):
                     mock_service.reset_mock()
+                    mock_service.global_service = None
                     inst = cls(session=backend_name)
                     mock_service.assert_called_once()
                     self.assertIsNone(inst.session)
@@ -230,6 +232,7 @@ def test_init_with_no_backend_session_cloud(self):
                 mock_service_inst.channel = "ibm_cloud"
                 mock_service.return_value = mock_service_inst
                 mock_service.reset_mock()
+                mock_service.global_service = None
                 inst = cls()
                 mock_service.assert_called_once()
                 self.assertIsNone(inst.session)

test/unit/test_session.py

@@ -18,11 +18,12 @@
 from qiskit_ibm_runtime.ibm_backend import IBMBackend
 from qiskit_ibm_runtime.exceptions import IBMInputValueError
 import qiskit_ibm_runtime.session as session_pkg
+from .mock.fake_runtime_service import FakeRuntimeService
 from ..ibm_test_case import IBMTestCase
 
 
 class TestSession(IBMTestCase):
-    """Class for testing the Session classession."""
+    """Class for testing the Session class."""
 
     def tearDown(self) -> None:
         super().tearDown()
@@ -31,6 +32,7 @@ def tearDown(self) -> None:
     @patch("qiskit_ibm_runtime.session.QiskitRuntimeService", autospec=True)
     def test_default_service(self, mock_service):
         """Test using default service."""
+        mock_service.global_service = None
         session = Session(backend="ibm_gotham")
         self.assertIsNotNone(session.service)
         mock_service.assert_called_once()
@@ -147,3 +149,17 @@ def test_default_backend(self):
         session = Session(service=service)
         session.run(program_id="foo", inputs={})
         self.assertEqual(session.backend(), "ibm_gotham")
+
+    def test_global_service(self):
+        """Test that global service is used in Session"""
+        _ = FakeRuntimeService(channel="ibm_quantum", token="abc")
+        session = Session(backend="ibmq_qasm_simulator")
+        self.assertTrue(isinstance(session._service, FakeRuntimeService))
+        self.assertEqual(session._service._account.token, "abc")
+        _ = FakeRuntimeService(channel="ibm_quantum", token="xyz")
+        session = Session(backend="ibmq_qasm_simulator")
+        self.assertEqual(session._service._account.token, "xyz")
+        with Session(
+            service=FakeRuntimeService(channel="ibm_quantum", token="uvw"), backend="ibm_gotham"
+        ) as session:
+            self.assertEqual(session._service._account.token, "uvw")