Simplify: deduplicate warning, fix lambda pattern, use direct attr access

- Extract duplicate C++ alpha_mode warning into shared
  warn_cpp_alpha_mode_unsupported() in validation.py
- Use outer-ternary lambda pattern consistently in Stokes branch
- Replace getattr() with direct attribute access on kWaveMedium dataclass

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: waltsims

kwave/kWaveSimulation_helper/save_to_disk_func.py

@@ -1,6 +1,5 @@
 import logging
 import os
-import warnings
 
 import numpy as np
 from scipy.io import savemat
@@ -230,15 +229,9 @@ def grab_medium_props(integer_variables, float_variables, medium, is_elastic_cod
         integer_variables.absorbing_flag = 0
 
     if medium.absorbing:
-        alpha_mode = getattr(medium, "alpha_mode", None)
-        if alpha_mode in ("no_absorption", "no_dispersion"):
-            warnings.warn(
-                f"medium.alpha_mode='{alpha_mode}' is not supported by the C++ backend "
-                f"and will be silently ignored. The C++ binary always computes both "
-                f"absorption and dispersion when absorbing_flag > 0. Use backend='python' "
-                f"to honor alpha_mode.",
-                stacklevel=4,
-            )
+        from kwave.solvers.validation import warn_cpp_alpha_mode_unsupported
+
+        warn_cpp_alpha_mode_unsupported(medium.alpha_mode, stacklevel=4)
         if is_elastic_code:  # pragma: no cover
             # add to the variable list
             float_variables["chi"] = None

kwave/solvers/cpp_simulation.py

@@ -37,15 +37,9 @@ def __init__(self, kgrid, medium, source, sensor, *, pml_size, pml_alpha, use_sg
         self.use_sg = use_sg
         self.ndim = kgrid.dim
 
-        alpha_mode = getattr(medium, "alpha_mode", None)
-        if alpha_mode in ("no_absorption", "no_dispersion"):
-            warnings.warn(
-                f"medium.alpha_mode='{alpha_mode}' is not supported by the C++ backend "
-                f"and will be silently ignored. The C++ binary always computes both "
-                f"absorption and dispersion when absorbing_flag > 0. Use backend='python' "
-                f"to honor alpha_mode.",
-                stacklevel=3,
-            )
+        from kwave.solvers.validation import warn_cpp_alpha_mode_unsupported
+
+        warn_cpp_alpha_mode_unsupported(medium.alpha_mode, stacklevel=3)
 
     def prepare(self, data_path=None):
         """Write HDF5 input file. Returns (input_file, output_file)."""

kwave/solvers/kspace_solver.py

@@ -411,7 +411,7 @@ def _setup_physics_operators(self):
 
         # Absorption/dispersion
         alpha_coeff_raw = getattr(self.medium, "alpha_coeff", 0)
-        alpha_mode = getattr(self.medium, "alpha_mode", None)
+        alpha_mode = self.medium.alpha_mode
         if not _is_enabled(alpha_coeff_raw):
             self._absorption = lambda div_u: 0
             self._dispersion = lambda rho: 0
@@ -424,7 +424,7 @@ def _setup_physics_operators(self):
             no_dispersion = alpha_mode == "no_dispersion"
 
             if abs(alpha_power - 2.0) < 1e-10:  # Stokes
-                self._absorption = lambda div_u: 0 if no_absorption else -2 * alpha_np * self.c0 * self.rho0 * div_u
+                self._absorption = (lambda div_u: 0) if no_absorption else (lambda div_u: -2 * alpha_np * self.c0 * self.rho0 * div_u)
                 self._dispersion = lambda rho: 0
             else:  # Power-law with fractional Laplacian
                 tau = -2 * alpha_np * self.c0 ** (alpha_power - 1)

kwave/solvers/validation.py

@@ -47,7 +47,7 @@ def validate_medium(medium, kgrid):
             power = float(np.asarray(medium.alpha_power).flat[0])
             if power < 0 or power > 3:
                 warnings.warn(f"medium.alpha_power={power} is outside typical range [0, 3].", stacklevel=3)
-            alpha_mode = getattr(medium, "alpha_mode", None)
+            alpha_mode = medium.alpha_mode
             if abs(power - 1.0) < 0.05 and alpha_mode != "no_dispersion":
                 raise ValueError(
                     f"medium.alpha_power={power} is too close to 1.0. The dispersion term "
@@ -106,6 +106,18 @@ def validate_source(source, kgrid):
         raise ValueError("All velocity source components must either be single (1D) or many (2D) time series.")
 
 
+def warn_cpp_alpha_mode_unsupported(alpha_mode, stacklevel=3):
+    """Warn that the C++ backend cannot honor medium.alpha_mode."""
+    if alpha_mode in ("no_absorption", "no_dispersion"):
+        warnings.warn(
+            f"medium.alpha_mode='{alpha_mode}' is not supported by the C++ backend "
+            f"and will be silently ignored. The C++ binary always computes both "
+            f"absorption and dispersion when absorbing_flag > 0. Use backend='python' "
+            f"to honor alpha_mode.",
+            stacklevel=stacklevel,
+        )
+
+
 def validate_sensor(sensor, kgrid):
     if sensor is None or not hasattr(sensor, "mask") or sensor.mask is None:
         return