Github user tdas commented on a diff in the pull request:
https://github.com/apache/spark/pull/2538#discussion_r18200872
--- Diff:
streaming/src/main/scala/org/apache/spark/streaming/api/python/PythonDStream.scala
---
@@ -0,0 +1,261 @@
+/*
+ * 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.
+ */
+
+package org.apache.spark.streaming.api.python
+
+import java.util.{ArrayList => JArrayList, List => JList}
+import scala.collection.JavaConversions._
+import scala.collection.JavaConverters._
+import scala.collection.mutable
+
+import org.apache.spark.api.java._
+import org.apache.spark.api.python._
+import org.apache.spark.rdd.RDD
+import org.apache.spark.storage.StorageLevel
+import org.apache.spark.streaming.{Interval, Duration, Time}
+import org.apache.spark.streaming.dstream._
+import org.apache.spark.streaming.api.java._
+
+
+/**
+ * Interface for Python callback function with three arguments
+ */
+trait PythonRDDFunction {
+ def call(time: Long, rdds: JList[_]): JavaRDD[Array[Byte]]
+}
+
+/**
+ * Wrapper for PythonRDDFunction
+ */
+private[python] class RDDFunction(pfunc: PythonRDDFunction)
--- End diff --
I think I get it. You need a simple trait / interface (`PythonRDDFunction`)
that is used as the interface for creating python function objects through
py4j. And then you need to convert it to a `Function2` object (using
`RDDFunction` class) so that it can be passed on to `DStream.foreachRDD`.
However, I am not sure this warrants a separate class with a confusing name.
How about static conversions added to `object PythonRDDFunction` like
```
object PythonRDDFunction {
implicit def toFunction2(): Option[Function2[....]] = {
}
}
```
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