rdblue commented on code in PR #5627:
URL: https://github.com/apache/iceberg/pull/5627#discussion_r956788070


##########
python/pyiceberg/schema.py:
##########
@@ -638,3 +724,61 @@ def map(self, map_type: MapType, key_result: int, 
value_result: int) -> int:
 
     def primitive(self, primitive: PrimitiveType) -> int:
         return 0
+
+
+def assign_fresh_schema_ids(schema: Schema) -> Schema:
+    """Traverses the schema, and sets new IDs"""
+    schema_struct = pre_order_visit(schema.as_struct(), _SetFreshIDs())
+
+    fresh_identifier_field_ids = []
+    new_schema = Schema(*schema_struct.fields)
+    for field_id in schema.identifier_field_ids:
+        original_field_name = schema.find_column_name(field_id)
+        if original_field_name is None:
+            raise ValueError(f"Could not find field: {field_id}")
+        fresh_field = new_schema.find_field(original_field_name)
+        if fresh_field is None:
+            raise ValueError(f"Could not lookup field in new schema: 
{original_field_name}")
+        fresh_identifier_field_ids.append(fresh_field.field_id)
+
+    return new_schema.copy(update={"identifier_field_ids": 
fresh_identifier_field_ids})
+
+
+class _SetFreshIDs(PreOrderSchemaVisitor[IcebergType]):
+    """Traverses the schema and assigns monotonically increasing ids"""
+
+    counter: itertools.count
+
+    def __init__(self, start: int = 1) -> None:
+        self.counter = itertools.count(start)
+
+    def _get_and_increment(self) -> int:
+        return next(self.counter)
+
+    def schema(self, schema: Schema, struct_result: Callable[[], StructType]) 
-> Schema:
+        return Schema(*struct_result().fields, 
identifier_field_ids=schema.identifier_field_ids)
+
+    def struct(self, struct: StructType, field_results: List[Callable[[], 
IcebergType]]) -> StructType:
+        return StructType(*[field() for field in field_results])
+
+    def field(self, field: NestedField, field_result: Callable[[], 
IcebergType]) -> IcebergType:
+        return NestedField(
+            field_id=self._get_and_increment(), name=field.name, 
field_type=field_result(), required=field.required, doc=field.doc

Review Comment:
   This is going to visit children before visiting the next field. If you're 
trying to match the behavior of assignment in Java, you'd need to [increment 
the counter for each field and then visit 
children](https://github.com/apache/iceberg/blob/master/api/src/main/java/org/apache/iceberg/types/AssignFreshIds.java#L80-L84).



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