From 5203640549e690672c1bea3a1aa9ebe6c4f47121 Mon Sep 17 00:00:00 2001
From: Jonathan Shimwell <mail@jshimwell.com>
Date: Thu, 9 Jul 2026 23:55:32 +0200
Subject: [PATCH] Further input validation for plot methods (#4004)

---
 openmc/model/model.py          | 14 +++++++++++++-
 tests/unit_tests/test_model.py | 21 +++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/openmc/model/model.py b/openmc/model/model.py
index 328494288..b166137f2 100644
--- a/openmc/model/model.py
+++ b/openmc/model/model.py
@@ -21,7 +21,8 @@ import openmc
 import openmc._xml as xml
 from openmc.dummy_comm import DummyCommunicator
 from openmc.executor import _process_CLI_arguments
-from openmc.checkvalue import check_type, check_value, PathLike
+from openmc.checkvalue import (check_type, check_value, check_greater_than,
+                               check_length, PathLike)
 from openmc.exceptions import InvalidIDError
 from openmc.plots import add_plot_params, _BASIS_INDICES, id_map_to_rgb
 from openmc.utility_funcs import change_directory
@@ -1050,6 +1051,13 @@ class Model:
         pixels: int | Sequence[int],
         basis: str
     ):
+        if isinstance(pixels, int):
+            check_greater_than('pixels', pixels, 0)
+        else:
+            check_length('pixels', pixels, 2)
+            for p in pixels:
+                check_greater_than('pixels', p, 0)
+
         x, y, _ = _BASIS_INDICES[basis]
 
         bb = self.bounding_box
@@ -1301,7 +1309,11 @@ class Model:
         import matplotlib.pyplot as plt
 
         check_type('n_samples', n_samples, int | None)
+        if n_samples is not None:
+            check_greater_than('n_samples', n_samples, 0, equality=True)
         check_type('plane_tolerance', plane_tolerance, Real)
+        check_greater_than('plane_tolerance', plane_tolerance, 0.0)
+
         if legend_kwargs is None:
             legend_kwargs = {}
         legend_kwargs.setdefault('bbox_to_anchor', (1.05, 1))
diff --git a/tests/unit_tests/test_model.py b/tests/unit_tests/test_model.py
index 028a83b0b..52ac43117 100644
--- a/tests/unit_tests/test_model.py
+++ b/tests/unit_tests/test_model.py
@@ -660,6 +660,27 @@ def test_model_plot():
     plt.close('all')
 
 
+def test_model_plot_invalid_inputs():
+    surface = openmc.Sphere(r=10.0, boundary_type="vacuum")
+    cell = openmc.Cell(region=-surface)
+    model = openmc.Model(openmc.Geometry([cell]))
+
+    with pytest.raises(ValueError):
+        model.plot(n_samples=-1)
+    with pytest.raises(TypeError):
+        model.plot(n_samples=1.5)
+    with pytest.raises(ValueError):
+        model.plot(plane_tolerance=0.0)
+    with pytest.raises(TypeError):
+        model.plot(plane_tolerance='1')
+    with pytest.raises(ValueError):
+        model.plot(pixels=-1)
+    with pytest.raises(ValueError):
+        model.plot(pixels=(0, 100))
+    with pytest.raises(ValueError):
+        model.plot(pixels=(100,))
+
+
 def test_model_id_map_initialization(run_in_tmpdir):
     model = openmc.examples.pwr_assembly()
     model.init_lib(output=False)