[GitHub] [iceberg] JonasJ-ap commented on a diff in pull request #7523: Python: Support Inferring Iceberg UUID type from parquet files

["JonasJ-ap (via GitHub)" <gi...@apache.org>]

JonasJ-ap commented on code in PR #7523:
URL: https://github.com/apache/iceberg/pull/7523#discussion_r1184538670


##########
python/pyiceberg/io/pyarrow.py:
##########
@@ -612,14 +612,40 @@ def _get_field_doc(field: pa.Field) -> Optional[str]:
 
 
 class _ConvertToIceberg(PyArrowSchemaVisitor[Union[IcebergType, Schema]]):
+    def __init__(self, expected_schema: Optional[Schema] = None):
+        self.expected_schema = expected_schema
+
+    def cast_if_needed(self, field_id: int, field_type: IcebergType) -> IcebergType:

Review Comment:
   An alternative solution (a simpler one) may be adding allowing promoting from `FixedType(16)` to `UUIDType` here:https://github.com/apache/iceberg/blob/3db4e896587d95318a690979e97bab55db250e23/python/pyiceberg/schema.py#L1308-L1322
   
   by adding 
   ```python
   @promote.register(FixedType)
   def _(file_type: FixedType, read_type: IcebergType) -> IcebergType:
       if isinstance(read_type, UUIDType) and len(file_type) == 16:
           return read_type
       else:
           raise ResolveError(f"Cannot promote an {file_type} to {read_type}")
   ```
   
   My concern here is that the added promotion is not listed as a valid type promotions in [spec](https://iceberg.apache.org/spec/#schema-evolution and the effect of the added promotion may be too large. So currently I chose to narrow the fix to the visitor. Looking forward to hearing more thoughts on this.



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