Fix Q3D results on fresh pandas installs

Author: shanto268

docs/source/release_notes.rst

@@ -1,6 +1,20 @@
 Release Notes
 =============
 
+Version 0.4.5 (Unreleased)
+--------------------------
+
+**Bug Fixes**
+
+- Capped ``pandas`` below 3.0 because ``pyEPR`` still uses the removed
+  ``read_csv(delim_whitespace=...)`` argument when parsing Q3D exported
+  capacitance matrices. Fresh installs could otherwise solve successfully in
+  Ansys, fail while loading the matrix, and surface as a confusing
+  ``NoneType`` simulation result.
+- ``AnsysSimulator.simulate`` now raises a clear ``RuntimeError`` if a
+  low-level simulation path returns no result payload, instead of printing
+  ``Simulation Completed Successfully!`` and returning ``None``.
+
 Version 0.4.4 (2026-04-19)
 --------------------------
 

pyproject.toml

@@ -24,7 +24,7 @@ dependencies = [
     "huggingface-hub>=0.21",
     # === Scientific Computing ===
     "numpy>=1.16.6,<2.0",
-    "pandas>=1.5",
+    "pandas>=1.5,<3.0",
     "scipy>=1.10",
     "numba>=0.60",
     "scqubits>=4.0",

squadds/simulations/ansys_simulator.py

@@ -401,6 +401,11 @@ def simulate(self, device_dict=None, run_async=False):
         self.console.rule("[bold cyan]Starting Simulation[/bold cyan]")
         try:
             result = self._run_simulation(device_dict)
+            if result is None:
+                raise RuntimeError(
+                    "Ansys simulation completed without a result payload. "
+                    "Check the Q3D/HFSS logs above for the root error."
+                )
             self.console.print("[bold green]Simulation Completed Successfully![/bold green]")
             return result
         except Exception as e:

tests/test_ansys_simulator.py

@@ -2,6 +2,9 @@
 from pathlib import Path
 from unittest.mock import patch
 
+import pytest
+
+import squadds.simulations.ansys_simulator as ansys_simulator_module
 from squadds.simulations.ansys_simulator import AnsysSimulator
 from squadds.simulations.drivenmodal.models import (
     CapacitanceExtractionRequest,
@@ -151,6 +154,24 @@ def test_normalize_device_dict_deserializes_json_like_payloads(headless_qiskit_e
     assert simulator.device_dict["setup_cavity_claw"] == {"max_passes": 15}
 
 
+def test_simulate_raises_when_low_level_simulation_returns_none(monkeypatch, headless_qiskit_environment):
+    simulator = AnsysSimulator(
+        DummyAnalyzer("qubit"),
+        {
+            "design_options": {"cross_length": "200um"},
+            "setup": {"max_passes": 1},
+        },
+    )
+
+    def fake_simulate_single_design(*args, **kwargs):
+        return None, None, None
+
+    monkeypatch.setattr(ansys_simulator_module, "simulate_single_design", fake_simulate_single_design)
+
+    with pytest.raises(RuntimeError, match="completed without a result payload"):
+        simulator.simulate()
+
+
 def test_run_drivenmodal_initializes_checkpoint_manifest(headless_qiskit_environment, tmp_path: Path):
     simulator = AnsysSimulator(
         DummyAnalyzer("qubit_claw"),

tests/test_dependency_constraints.py

@@ -0,0 +1,8 @@
+from pathlib import Path
+
+
+def test_pandas_is_capped_below_three_until_pyepr_matrix_parser_is_updated():
+    pyproject = Path("pyproject.toml").read_text()
+    pandas_specs = [line.strip().strip('",') for line in pyproject.splitlines() if '"pandas' in line]
+
+    assert pandas_specs == ["pandas>=1.5,<3.0"]