Fix conversion options validation failing on type and callable objects

CHANGELOG.md

@@ -17,6 +17,7 @@
 * Deprecated returning NWBFile when using `append_on_disk_nwbfile=True` in `write_imaging_to_nwbfile` and `write_segmentation_to_nwbfile`. Will return None on or after June 2026. [PR #1649](https://github.com/catalystneuro/neuroconv/pull/1649)
 
 ## Bug Fixes
+* Fixed `TypeError: Object of type type is not JSON serializable` when passing `type` or `callable` objects (e.g. `progress_bar_class`) in `conversion_options`. The validation step now serializes these to their qualified module path for JSON schema validation while passing the original objects through to conversion unchanged. [PR #1667](https://github.com/catalystneuro/neuroconv/pull/1667)
 * Fixed `UnicodeDecodeError` on Windows when reading YAML and JSON files containing UTF-8 characters by adding explicit `encoding='utf-8'` parameter to all text file operations. This ensures cross-platform compatibility per PEP 597 recommendations. [PR #1657](https://github.com/catalystneuro/neuroconv/pull/1657)
 * Fixed bug in `write_imaging_to_nwbfile` where `nwbfile` was incorrectly passed to `add_imaging_to_nwbfile` instead of the created/loaded nwbfile. [PR #1649](https://github.com/catalystneuro/neuroconv/pull/1649)
 * Fixed bug in `write_segmentation_to_nwbfile` where invalid `plane_num` parameter was passed to `add_segmentation_to_nwbfile`. [PR #1649](https://github.com/catalystneuro/neuroconv/pull/1649)

src/neuroconv/utils/json_schema.py

@@ -60,6 +60,17 @@ class _NWBConversionOptionsEncoder(_GenericNeuroconvEncoder):
     Custom JSON encoder for conversion options of the data interfaces and converters (i.e. kwargs).
     """
 
+    def default(self, obj):
+        # Serialize classes to their qualified name (e.g. progress_bar_class in iterator_options)
+        if isinstance(obj, type):
+            return f"{obj.__module__}.{obj.__qualname__}"
+
+        # Serialize callable objects (e.g. callback functions in progress_bar_options)
+        if callable(obj):
+            return f"{obj.__module__}.{obj.__qualname__}"
+
+        return super().default(obj)
+
 
 # This is used in the Guide so we will keep it public.
 NWBMetaDataEncoder = _NWBMetaDataEncoder

tests/test_minimal/test_interface_validation.py

@@ -27,3 +27,57 @@ def add_to_nwbfile(self, nwbfile: NWBFile, metadata: dict | None, datetime_optio
 
     nwbfile_path = tmp_path / "converter_test.nwb"
     converter.run_conversion(nwbfile_path=nwbfile_path, overwrite=True, conversion_options=conversion_options)
+
+
+def test_conversion_options_validation_with_type_and_callable(tmp_path):
+    """Test that type objects and callables in conversion_options don't break validation.
+
+    This is a regression test for https://github.com/catalystneuro/neuroconv/pull/1667.
+    NWB GUIDE passes progress_bar_class (a type) and callback functions nested inside
+    iterator_opts dict in conversion_options, which caused TypeError during JSON
+    serialization in the validation step.
+    """
+
+    class InterfaceWithIteratorOpts(MockInterface):
+
+        def add_to_nwbfile(
+            self,
+            nwbfile: NWBFile,
+            metadata: dict | None,
+            iterator_opts: dict | None = None,
+        ):
+            pass
+
+    class MyProgressBar:
+        pass
+
+    def my_callback():
+        pass
+
+    iterator_opts = dict(
+        display_progress=True,
+        progress_bar_class=MyProgressBar,
+        progress_bar_options=dict(callback=my_callback),
+    )
+
+    interface = InterfaceWithIteratorOpts()
+
+    # Test with type object and callable via interface.run_conversion
+    nwbfile_path = tmp_path / "interface_test.nwb"
+    interface.run_conversion(
+        nwbfile_path=nwbfile_path,
+        iterator_opts=iterator_opts,
+        overwrite=True,
+    )
+
+    # Test with type object and callable via ConverterPipe.run_conversion
+    data_interfaces = {"InterfaceWithIteratorOpts": interface}
+    conversion_options = {
+        "InterfaceWithIteratorOpts": {
+            "iterator_opts": iterator_opts,
+        }
+    }
+    converter = ConverterPipe(data_interfaces=data_interfaces)
+
+    nwbfile_path = tmp_path / "converter_test.nwb"
+    converter.run_conversion(nwbfile_path=nwbfile_path, overwrite=True, conversion_options=conversion_options)