fix: handle OptionalImportError for class-based reader instantiation

The exception handling for missing optional packages only wrapped string-based
reader imports (LoadImage(reader='ITKReader')). When users passed a class directly
(LoadImage(reader=ITKReader)), OptionalImportError would leak through.

Update the class instantiation path (elif inspect.isclass(_r):) to:
1. Catch OptionalImportError during _r(*args, **kwargs) call
2. Re-raise as RuntimeError with consistent message
3. Use exception chaining (from e) for debugging
4. Handle TypeError with warn-and-retry (same as string path)
5. Extract class name safely for error message

Now both LoadImage(reader='ITKReader') and LoadImage(reader=ITKReader) produce
consistent RuntimeError when the optional package is missing.

Add test_explicit_class_reader_not_installed_raises_runtime_error to verify
the class path is properly handled.

Signed-off-by: Cipher <cipher@openclaw.ai>

Author: Cipher

monai/transforms/io/array.py

@@ -219,7 +219,18 @@ def __init__(
                     warnings.warn(f"{_r} is not supported with the given parameters {args} {kwargs}.")
                     self.register(the_reader())
             elif inspect.isclass(_r):
-                self.register(_r(*args, **kwargs))
+                try:
+                    self.register(_r(*args, **kwargs))
+                except OptionalImportError as e:
+                    reader_name = getattr(_r, "__name__", str(_r))
+                    raise RuntimeError(
+                        f"The required package for reader '{reader_name}' is not installed, or the version doesn't match "
+                        f"the requirement. If you want to use '{reader_name}', please install the required package. "
+                        f"If you want to use an alternative reader, do not specify the `reader` argument."
+                    ) from e
+                except TypeError:  # the reader doesn't have the corresponding args/kwargs
+                    warnings.warn(f"{_r.__name__} is not supported with the given parameters {args} {kwargs}.")
+                    self.register(_r())
             else:
                 self.register(_r)  # reader instance, ignoring the constructor args/kwargs
         return

tests/transforms/test_load_image.py

@@ -514,6 +514,15 @@ def test_explicit_reader_not_installed_raises_runtime_error(self):
         self.assertIn("ITKReader", str(ctx.exception))
         self.assertIn("not installed", str(ctx.exception))
 
+    def test_explicit_class_reader_not_installed_raises_runtime_error(self):
+        """When user passes a class reader whose package is missing, RuntimeError is raised (not OptionalImportError)."""
+        # This tests the class path (not string path) to ensure consistent behavior
+        with patch("monai.data.ITKReader.__init__", side_effect=OptionalImportError("itk")):
+            with self.assertRaises(RuntimeError) as ctx:
+                LoadImage(reader=ITKReader)
+            self.assertIn("ITKReader", str(ctx.exception))
+            self.assertIn("not installed", str(ctx.exception))
+
     def test_unspecified_reader_falls_back_silently(self):
         """When no reader is specified, missing optional readers should be silently skipped (no exception)."""
         # Force the fallback path by simulating missing optional dependencies.