[GitHub] [spark] dstrodtman-db commented on a diff in pull request #42272: [SPARK-44508][PYTHON][DOCS] Add user guide for Python user-defined table functions

["dstrodtman-db (via GitHub)" <gi...@apache.org>]

dstrodtman-db commented on code in PR #42272:
URL: https://github.com/apache/spark/pull/42272#discussion_r1287312350


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python/docs/source/user_guide/sql/python_udtf.rst:
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+..  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.
+
+===========================================
+Python User-defined Table Functions (UDTFs)
+===========================================
+
+Spark 3.5 introduces Python user-defined table functions (UDTFs), a new type of user-defined function. 
+Unlike scalar functions that return a single result value, a UDTF is invoked in the FROM clause and returns 
+an entire relation as output. Each UDTF call can accept zero or more arguments. 
+These arguments can be scalar constant expressions or separate input relations.
+
+Implementing a Python UDTF
+--------------------------
+
+.. currentmodule:: pyspark.sql.functions
+
+To implement a Python UDTF, you can define a class implementing the methods:
+
+.. code-block:: python
+
+    class PythonUDTF:
+
+        def __init__(self) -> None:
+            """
+            Initialize the user-defined table function (UDTF).
+
+            This method serves as the default constructor and is called once when the
+            UDTF is instantiated on the executor side. Although its implementation is
+            optional, it can be for any necessary initialization, such as setting up
+            resources or state for the UDTF.
+            
+            Any class fields assigned in this method will be available for subsequent
+            calls to the `eval` and `terminate` methods.
+
+            Notes
+            -----
+            - This method does not accept any extra arguments.
+            - You cannot reference the Spark session within the UDTF. Any attempt to
+              do so will result in a serialization error.
+            """
+            ...
+
+        def eval(self, *args: Any) -> Iterator[Any]:
+            """
+            Evaluate the function using the given input arguments.
+
+            This method is required and must be implemented.
+            
+            The arguments provided to the UDTF call are mapped to the values in the
+            `*args` list sequentially. Each provided scalar expression maps to exactly
+            one value in this `*args` list. Each provided TABLE argument of N columns
+            maps to exactly N values in this `*args` list, in the order of the columns
+            as they appear in the table.
+
+            This method is called on every input row, and can produce zero or more
+            output rows. Each element in the tuple will correspond to one column
+            specified in the return type of the UDTF.
+
+            Parameters
+            ----------
+            *args : Any
+                Arbitrary positional arguments representing the input to the UDTF.
+
+            Yields
+            ------
+            tuple
+                A tuple representing a single row in the UDTF result relation.
+                Yield as many times as needed to produce multiple rows.
+
+            Notes
+            -----
+            - The result of the function must be a tuple representing a single row
+              in the UDTF result relation.
+            - UDTFs do not ccept keyword arguments during the function call.

Review Comment:
   ```suggestion
               - UDTFs do not accept keyword arguments during the function call.
   ```



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