diff --git a/python/pyspark/streaming/dstream.py b/python/pyspark/streaming/dstream.py
index d98afc3e5a294..d866f8c9687fb 100644
--- a/python/pyspark/streaming/dstream.py
+++ b/python/pyspark/streaming/dstream.py
@@ -552,14 +552,18 @@ def reduceByKeyAndWindow(self, func, invFunc, windowDuration, slideDuration=None
 
         def reduceFunc(t, a, b):
             b = b.reduceByKey(func, numPartitions)
-            r = a.union(b).reduceByKey(func, numPartitions) if a else b
+            # use the average of number of partitions, or it will keep increasing
+            partitions = numPartitions or (a.getNumPartitions() + b.getNumPartitions())/2
+            r = a.union(b).reduceByKey(func, partitions) if a else b
             if filterFunc:
                 r = r.filter(filterFunc)
             return r
 
         def invReduceFunc(t, a, b):
             b = b.reduceByKey(func, numPartitions)
-            joined = a.leftOuterJoin(b, numPartitions)
+            # use the average of number of partitions, or it will keep increasing
+            partitions = numPartitions or (a.getNumPartitions() + b.getNumPartitions())/2
+            joined = a.leftOuterJoin(b, partitions)
             return joined.mapValues(lambda (v1, v2): invFunc(v1, v2) if v2 is not None else v1)
 
         jreduceFunc = RDDFunction(self.ctx, reduceFunc, reduced._jrdd_deserializer)
@@ -587,7 +591,9 @@ def reduceFunc(t, a, b):
             if a is None:
                 g = b.groupByKey(numPartitions).map(lambda (k, vs): (k, list(vs), None))
             else:
-                g = a.cogroup(b, numPartitions)
+                # use the average of number of partitions, or it will keep increasing
+                partitions = numPartitions or (a.getNumPartitions() + b.getNumPartitions())/2
+                g = a.cogroup(b, partitions)
                 g = g.map(lambda (k, (va, vb)): (k, list(vb), list(va)[0] if len(va) else None))
             state = g.mapPartitions(lambda x: updateFunc(x))
             return state.filter(lambda (k, v): v is not None)
diff --git a/python/pyspark/streaming/tests.py b/python/pyspark/streaming/tests.py
index 7ffdb145c104e..0dc6b3d675397 100644
--- a/python/pyspark/streaming/tests.py
+++ b/python/pyspark/streaming/tests.py
@@ -22,7 +22,7 @@
 import unittest
 import tempfile
 
-from pyspark.context import SparkContext
+from pyspark.context import SparkContext, RDD
 from pyspark.streaming.context import StreamingContext
 
 
@@ -46,8 +46,13 @@ def _test_func(self, input, func, expected, sort=False, input2=None):
         @param func: wrapped function. This function should return PythonDStream object.
         @param expected: expected output for this testcase.
         """
+        if not isinstance(input[0], RDD):
+            input = [self.sc.parallelize(d, 1) for d in input]
         input_stream = self.ssc.queueStream(input)
+        if input2 and not isinstance(input2[0], RDD):
+            input2 = [self.sc.parallelize(d, 1) for d in input2]
         input_stream2 = self.ssc.queueStream(input2) if input2 is not None else None
+
         # Apply test function to stream.
         if input2:
             stream = func(input_stream, input_stream2)
@@ -63,6 +68,7 @@ def _test_func(self, input, func, expected, sort=False, input2=None):
             current_time = time.time()
             # Check time out.
             if (current_time - start_time) > self.timeout:
+                print "timeout after", self.timeout
                 break
             # StreamingContext.awaitTermination is not used to wait because
             # if py4j server is called every 50 milliseconds, it gets an error.