Address code review feedback: improve None handling and add title truncation logic

Co-authored-by: jnumainville <[email protected]>

Author: Copilot

plugins/plotly-express/src/deephaven/plot/express/plots/subplots.py

@@ -398,16 +398,21 @@ def atomic_make_subplots(
                     final_subplot_titles.append("")
                 else:
                     extracted_title = extract_title_from_figure(fig)
+                    # Explicitly check for None to handle empty strings correctly
                     final_subplot_titles.append(
-                        extracted_title if extracted_title else ""
+                        extracted_title if extracted_title is not None else ""
                     )
     elif subplot_titles is not None:
         # Convert to list if tuple
         final_subplot_titles = list(subplot_titles)
 
-        # Pad with empty strings if needed
+        # Validate and adjust length if needed
         total_subplots = rows * cols
-        if len(final_subplot_titles) < total_subplots:
+        if len(final_subplot_titles) > total_subplots:
+            # Truncate if too many titles provided
+            final_subplot_titles = final_subplot_titles[:total_subplots]
+        elif len(final_subplot_titles) < total_subplots:
+            # Pad with empty strings if too few titles provided
             final_subplot_titles.extend(
                 [""] * (total_subplots - len(final_subplot_titles))
             )

plugins/plotly-express/test/deephaven/plot/express/plots/test_make_subplots.py

@@ -715,6 +715,26 @@ def test_make_subplots_conflicting_title_options(self):
 
         self.assertIn("Cannot use both", str(context.exception))
 
+    def test_make_subplots_with_too_many_subplot_titles(self):
+        import src.deephaven.plot.express as dx
+
+        chart = dx.scatter(self.source, x="X", y="Y")
+        # Provide more titles than subplots - should be truncated
+        charts = dx.make_subplots(
+            chart,
+            chart,
+            rows=2,
+            subplot_titles=["Plot 1", "Plot 2", "Plot 3", "Plot 4"],
+        ).to_dict(self.exporter)
+
+        # Check that only 2 annotations were created (truncated)
+        layout = charts["plotly"]["layout"]
+        self.assertIn("annotations", layout)
+        annotations = layout["annotations"]
+        self.assertEqual(len(annotations), 2)
+        self.assertEqual(annotations[0]["text"], "Plot 1")
+        self.assertEqual(annotations[1]["text"], "Plot 2")
+
 
 if __name__ == "__main__":
     unittest.main()