[GitHub] [arrow] paleolimbot commented on a diff in pull request #35568: GH-33986: [Python] Add a minimal protocol for datasets

["paleolimbot (via GitHub)" <gi...@apache.org>]

paleolimbot commented on code in PR #35568:
URL: https://github.com/apache/arrow/pull/35568#discussion_r1237865263


##########
python/pyarrow/dataset/protocol.py:
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@@ -0,0 +1,77 @@
+# 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.
+"""Protocol definitions for pyarrow.dataset
+
+These provide the abstract interface for a dataset. Other libraries may implement
+this interface to expose their data, without having to extend PyArrow's classes.
+
+Applications and libraries that want to consume datasets should accept datasets
+that implement these protocols, rather than requiring the specific
+PyArrow classes.
+"""
+from abc import abstractmethod
+from typing import Iterator, List, Optional, Protocol
+
+from pyarrow.dataset import Expression
+from pyarrow import Table, IntegerArray, RecordBatch, RecordBatchReader, Schema
+
+
+class Scanner(Protocol):
+    @abstractmethod
+    def count_rows(self) -> int:
+        ...
+    
+    @abstractmethod
+    def head(self, num_rows: int) -> Table:
+        ...
+
+    @abstractmethod
+    def take(self, indices: IntegerArray) -> Table:
+        ...
+    
+    @abstractmethod
+    def to_table(self) -> Table:
+        ...
+    
+    @abstractmethod
+    def to_batches(self) -> Iterator[RecordBatch]:
+        ...
+
+    @abstractmethod
+    def to_reader(self) -> RecordBatchReader:
+        ...
+
+
+class Scannable(Protocol):
+    @abstractmethod
+    def scanner(self, columns: Optional[List[str]] = None,
+                filter: Optional[Expression] = None, **kwargs) -> Scanner:

Review Comment:
   I'm an obvious Arrow C interface junkie, but I quite like the idea of this. It would also mean that duckdb, datafusion, polars etc. would be able to implement the protocol once without having to reinvent a way to represent a syntax tree in each language binding.



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