Fixed bug in deepcopy of IBMBackend (#902)

* Fixed infinite recursion when attempting to deepcopy an IBMBackend

* Moved test to integration tests

* Cleaned up deepcopy and relevant test

* Improved release notes

* Lint and Style

* black

* lint

---------

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

qiskit_ibm_runtime/ibm_backend.py

@@ -16,6 +16,7 @@
 
 from typing import Iterable, Union, Optional, Any, List
 from datetime import datetime as python_datetime
+from copy import deepcopy
 
 from qiskit import QuantumCircuit
 from qiskit.qobj.utils import MeasLevel, MeasReturnType
@@ -199,6 +200,11 @@ def __getattr__(self, name: str) -> Any:
         This magic method executes when user accesses an attribute that
         does not yet exist on IBMBackend class.
         """
+        # Prevent recursion since these properties are accessed within __getattr__
+        if name in ["_properties", "_defaults", "_target", "_configuration"]:
+            raise AttributeError(
+                "'{}' object has no attribute '{}'".format(self.__class__.__name__, name)
+            )
         # Lazy load properties and pulse defaults and construct the target object.
         self._get_properties()
         self._get_defaults()
@@ -529,6 +535,24 @@ def check_faulty(self, circuit: QuantumCircuit) -> None:
                     f"{instr} operating on a faulty edge {qubit_indices}"
                 )
 
+    def __deepcopy__(self, _memo: dict = None) -> "IBMBackend":
+        cpy = IBMBackend(
+            configuration=deepcopy(self.configuration()),
+            service=self._service,
+            api_client=deepcopy(self._api_client),
+            instance=self._instance,
+        )
+        cpy.name = self.name
+        cpy.description = self.description
+        cpy.online_date = self.online_date
+        cpy.backend_version = self.backend_version
+        cpy._coupling_map = self._coupling_map
+        cpy._defaults = deepcopy(self._defaults, _memo)
+        cpy._target = deepcopy(self._target, _memo)
+        cpy._max_circuits = self._max_circuits
+        cpy._options = deepcopy(self._options, _memo)
+        return cpy
+
 
 class IBMRetiredBackend(IBMBackend):
     """Backend class interfacing with an IBM Quantum device no longer available."""

releasenotes/notes/backend_deepcopy-965f6a19a6d17cb2.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+     Fixed infinite recursion when attempting to deepcopy an IBMBackend. Added
+     a method :meth:`qiskit_ibm_runtime.IBMBackend.deepcopy`.
+

test/integration/test_backend.py

@@ -13,7 +13,7 @@
 """Tests for backend functions using real runtime service."""
 
 from unittest import SkipTest
-
+import copy
 
 from qiskit.transpiler.target import Target
 from qiskit_ibm_runtime import QiskitRuntimeService
@@ -163,3 +163,25 @@ def test_backend_run(self):
         with self.subTest(backend=backend.name):
             with self.assertRaises(RuntimeError):
                 backend.run()
+
+    def test_backend_deepcopy(self):
+        """Test that deepcopy on IBMBackend works correctly"""
+        backend = self.backend
+        with self.subTest(backend=backend.name):
+            backend_copy = copy.deepcopy(backend)
+            self.assertEqual(backend_copy.name, backend.name)
+            self.assertEqual(
+                backend_copy.configuration().basis_gates,
+                backend.configuration().basis_gates,
+            )
+            self.assertEqual(
+                backend_copy.properties().last_update_date,
+                backend.properties().last_update_date,
+            )
+            self.assertEqual(backend_copy._instance, backend._instance)
+            self.assertEqual(backend_copy._service._backends, backend._service._backends)
+            self.assertEqual(backend_copy._get_defaults(), backend._get_defaults())
+            self.assertEqual(
+                backend_copy._api_client._session.base_url,
+                backend._api_client._session.base_url,
+            )