[Streaming] Union api (#8612)

streaming/python/runtime/gateway_client.py

@@ -30,7 +30,7 @@ class GatewayClient:
 
     def create_py_stream_source(self, serialized_func):
         assert isinstance(serialized_func, bytes)
-        call = self._python_gateway_actor.createPythonStreamSource\
+        call = self._python_gateway_actor.createPythonStreamSource \
             .remote(serialized_func)
         return deserialize(ray.get(call))
 
@@ -41,10 +41,16 @@ class GatewayClient:
 
     def create_py_partition(self, serialized_partition):
         assert isinstance(serialized_partition, bytes)
-        call = self._python_gateway_actor.createPyPartition\
+        call = self._python_gateway_actor.createPyPartition \
             .remote(serialized_partition)
         return deserialize(ray.get(call))
 
+    def union(self, *streams):
+        serialized_streams = serialize(streams)
+        call = self._python_gateway_actor.union \
+            .remote(serialized_streams)
+        return deserialize(ray.get(call))
+
     def call_function(self, java_class, java_function, *args):
         java_params = serialize([java_class, java_function] + list(args))
         call = self._python_gateway_actor.callFunction.remote(java_params)

streaming/python/runtime/graph.py

@@ -5,7 +5,6 @@ import ray.streaming.generated.remote_call_pb2 as remote_call_pb
 import ray.streaming.generated.streaming_pb2 as streaming_pb
 import ray.streaming.operator as operator
 import ray.streaming.partition as partition
-from ray.streaming import function
 from ray.streaming.generated.streaming_pb2 import Language
 
 
@@ -32,9 +31,8 @@ class ExecutionNode:
             node_pb.node_type)]
         self.parallelism = node_pb.parallelism
         if node_pb.language == Language.PYTHON:
-            func_bytes = node_pb.function  # python function descriptor
-            func = function.load_function(func_bytes)
-            self.stream_operator = operator.create_operator(func)
+            operator_bytes = node_pb.operator  # python operator descriptor
+            self.stream_operator = operator.load_operator(operator_bytes)
         self.execution_tasks = [
             ExecutionTask(task) for task in node_pb.execution_tasks
         ]