fix: raise TypeError for unsupported partition source type

The singledispatch fallback of _to_partition_representation used
return TypeError(...) instead of raise TypeError(...). For an
unsupported (non-primitive) partition source type this returned the
exception instance as the partition value instead of raising, so the
error would surface far from its cause. Raise it, and add a regression
test covering the base handler.

Signed-off-by: Anas Khan <83116240+anxkhn@users.noreply.github.com>

Author: anxkhn

pyiceberg/partitioning.py

@@ -500,7 +500,7 @@ def _to_partition_representation(type: IcebergType, value: Any) -> Any:
     can return date that still needs to be transformed into an int (days
     since epoch).
     """
-    return TypeError(f"Unsupported partition field type: {type}")
+    raise TypeError(f"Unsupported partition field type: {type}")
 
 
 @_to_partition_representation.register(TimestampType)

tests/table/test_partitioning.py

@@ -22,7 +22,12 @@
 import pytest
 
 from pyiceberg.exceptions import ValidationError
-from pyiceberg.partitioning import UNPARTITIONED_PARTITION_SPEC, PartitionField, PartitionSpec
+from pyiceberg.partitioning import (
+    UNPARTITIONED_PARTITION_SPEC,
+    PartitionField,
+    PartitionSpec,
+    _to_partition_representation,
+)
 from pyiceberg.schema import Schema
 from pyiceberg.transforms import (
     BucketTransform,
@@ -253,6 +258,13 @@ def test_transform_consistency_with_pyarrow_transform(source_type: PrimitiveType
             assert t.transform(source_type)(value) == t.pyarrow_transform(source_type)(pa.array([value])).to_pylist()[0]
 
 
+def test_to_partition_representation_unsupported_type() -> None:
+    unsupported_type = StructType(NestedField(1, "x", StringType()))
+
+    with pytest.raises(TypeError, match="Unsupported partition field type: struct"):
+        _to_partition_representation(unsupported_type, "value")
+
+
 def test_deserialize_partition_field_v2() -> None:
     json_partition_spec = """{"source-id": 1, "field-id": 1000, "transform": "truncate[19]", "name": "str_truncate"}"""