update comment

python/pyspark/streaming/dstream.py

@@ -1,3 +1,20 @@
+#
+# 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.
+#
+
 from collections import defaultdict
 from itertools import chain, ifilter, imap
 import operator
@@ -20,11 +37,13 @@ def __init__(self, jdstream, ssc, jrdd_deserializer):
 
     def count(self):
         """
+        Return a new DStream which contains the number of elements in this DStream.
         """
         return self._mapPartitions(lambda i: [sum(1 for _ in i)])._sum()
 
     def _sum(self):
         """
+        Add up the elements in this DStream.
         """
         return self._mapPartitions(lambda x: [sum(x)]).reduce(operator.add)
 
@@ -41,7 +60,7 @@ def print_(self):
 
     def filter(self, f):
         """
-        Return DStream containing only the elements that satisfy predicate.
+        Return a new DStream containing only the elements that satisfy predicate.
         """
         def func(iterator): return ifilter(f, iterator)
         return self._mapPartitions(func)
@@ -56,7 +75,7 @@ def func(s, iterator): return chain.from_iterable(imap(f, iterator))
 
     def map(self, f):
         """
-        Return DStream by applying a function to each element of DStream.
+        Return a new DStream by applying a function to each element of DStream.
         """
         def func(iterator): return imap(f, iterator)
         return self._mapPartitions(func)
@@ -71,12 +90,14 @@ def func(s, iterator): return f(iterator)
     def _mapPartitionsWithIndex(self, f, preservesPartitioning=False):
         """
         Return a new DStream by applying a function to each partition of this DStream,
-        While tracking the index of the original partition.
+        while tracking the index of the original partition.
         """
         return PipelinedDStream(self, f, preservesPartitioning)
 
     def reduce(self, func):
         """
+        Return a new DStream by reduceing the elements of this RDD using the specified
+        commutative and associative binary operator.
         """
         return self.map(lambda x: (None, x)).reduceByKey(func, 1).map(lambda x: x[1])
 
@@ -280,4 +301,3 @@ def _jdstream(self):
 
     def _is_pipelinable(self):
         return not (self.is_cached)
-