[GitHub] [iceberg] jun-he commented on a change in pull request #2697: [python] Adding Unknown and Void transforms

[GitBox <gi...@apache.org>]

jun-he commented on a change in pull request #2697:
URL: https://github.com/apache/iceberg/pull/2697#discussion_r652371530



##########
File path: python/iceberg/api/transforms/unknown_transform.py
##########
@@ -0,0 +1,61 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+from typing import Union
+
+from iceberg.api.types import StringType, Type
+
+from .transform import Transform
+
+
+class UnknownTransform(Transform):
+
+    def __init__(self, source_type: Type, transform: str):
+        self.source_type = source_type
+        self.transform = transform

Review comment:
       Similar to Java implementation, `__str__` should return `transform`.
   

##########
File path: python/iceberg/api/transforms/unknown_transform.py
##########
@@ -0,0 +1,61 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+from typing import Union
+
+from iceberg.api.types import StringType, Type
+
+from .transform import Transform
+
+
+class UnknownTransform(Transform):
+
+    def __init__(self, source_type: Type, transform: str):
+        self.source_type = source_type
+        self.transform = transform
+
+    def apply(self, value):
+        raise AttributeError(f"Cannot apply unsupported transform: {self.transform}")
+
+    def can_transform(self, type_var) -> bool:
+        # assume the transform function can be applied for this type because unknown transform is only used when parsing
+        # a transform in an existing table. a different Iceberg version must have already validated it.
+        return self.source_type == type_var
+
+    def get_result_type(self, source_type):
+        # the actual result type is not known
+        return StringType.get()
+
+    def project(self, name, predicate):
+        return None
+
+    def project_strict(self, name, predicate):
+        return None
+
+    def to_human_string(self, value) -> str:
+        return self.transform

Review comment:
       This should return `value` in string format instead of `transform`.




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