fix(#49): log warnings instead of silently swallowing backend property errors

src/qc_compiler/utils.py

@@ -4,9 +4,13 @@
 extraction used across all optimization modules.
 """
 
+import logging
+
 from qiskit import QuantumCircuit
 from qiskit.providers import BackendV2
 
+logger = logging.getLogger(__name__)
+
 TWO_QUBIT_GATES = {"cx", "cz", "ecr", "swap", "rxx", "rzz", "ryy", "crx", "cry", "crz"}
 
 
@@ -43,20 +47,20 @@ def get_backend_properties(backend: BackendV2) -> dict:
         try:
             t1_val = props.qubit_property(qubit, "T1")[0]
             t1_times[qubit] = float(t1_val)
-        except Exception:  # noqa: S110, BLE001
-            pass
+        except Exception:  # noqa: BLE001
+            logger.warning("Could not extract T1 for qubit %d", qubit)
 
         try:
             t2_val = props.qubit_property(qubit, "T2")[0]
             t2_times[qubit] = float(t2_val)
-        except Exception:  # noqa: S110, BLE001
-            pass
+        except Exception:  # noqa: BLE001
+            logger.warning("Could not extract T2 for qubit %d", qubit)
 
         try:
             ro_val = props.qubit_property(qubit, "readout_error")[0]
             readout_errors[qubit] = float(ro_val)
-        except Exception:  # noqa: S110, BLE001
-            pass
+        except Exception:  # noqa: BLE001
+            logger.warning("Could not extract readout error for qubit %d", qubit)
 
     single_qubit_gate_errors = {}
     two_qubit_gate_errors = {}

tests/test_utils.py

@@ -1,5 +1,8 @@
 """Tests for qc_compiler.utils module."""
 
+import logging
+from unittest.mock import MagicMock
+
 from qiskit import QuantumCircuit
 from qiskit_ibm_runtime.fake_provider import FakeBrisbane
 
@@ -366,4 +369,35 @@ def test_gate_length_unit_conversion(self):
         props = get_backend_properties(backend)
         assert len(props["gate_lengths"]) > 0
         for length in props["gate_lengths"].values():
-            assert length > 0
+            assert length > 0
+
+
+class TestBackendPropertyExtractionWarnings:
+    """Regression tests for backend property extraction logging (issue #49)."""
+
+    def test_missing_t1_logs_warning(self, caplog):
+        backend = MagicMock()
+        backend.name = "test_backend"
+        backend.num_qubits = 2
+        mock_props = MagicMock()
+        mock_props.qubit_property.side_effect = Exception("no T1 data")
+        mock_props.gates = []
+        backend.properties.return_value = mock_props
+
+        with caplog.at_level(logging.WARNING, logger="qc_compiler.utils"):
+            result = get_backend_properties(backend)
+        assert "Could not extract T1" in caplog.text
+        assert result["t1_times"] == {}
+
+    def test_missing_readout_error_logs_warning(self, caplog):
+        backend = MagicMock()
+        backend.name = "test_backend"
+        backend.num_qubits = 2
+        mock_props = MagicMock()
+        mock_props.qubit_property.side_effect = Exception("no data")
+        mock_props.gates = []
+        backend.properties.return_value = mock_props
+
+        with caplog.at_level(logging.WARNING, logger="qc_compiler.utils"):
+            get_backend_properties(backend)
+        assert "Could not extract readout error" in caplog.text