[SPARK-9812] [STREAMING] Fix Python 3 compatibility issue in PySpark Streaming and some docs

This PR includes the following fixes:
1. Use `range` instead of `xrange` in `queue_stream.py` to support Python 3.
2. Fix the issue that `utf8_decoder` will return `bytes` rather than `str` when receiving an empty `bytes` in Python 3.
3. Fix the commands in docs so that the user can copy them directly to the command line. The previous commands was broken in the middle of a path, so when copying to the command line, the path would be split to two parts by the extra spaces, which forces the user to fix it manually.

Author: zsxwing <zsxwing@gmail.com>

Closes #8315 from zsxwing/SPARK-9812.

examples/src/main/python/streaming/direct_kafka_wordcount.py

@@ -23,8 +23,8 @@
  http://kafka.apache.org/documentation.html#quickstart
 
  and then run the example
-    `$ bin/spark-submit --jars external/kafka-assembly/target/scala-*/\
-      spark-streaming-kafka-assembly-*.jar \
+    `$ bin/spark-submit --jars \
+      external/kafka-assembly/target/scala-*/spark-streaming-kafka-assembly-*.jar \
       examples/src/main/python/streaming/direct_kafka_wordcount.py \
       localhost:9092 test`
 """
@@ -37,7 +37,7 @@ from pyspark.streaming.kafka import KafkaUtils
 
 if __name__ == "__main__":
     if len(sys.argv) != 3:
-        print >> sys.stderr, "Usage: direct_kafka_wordcount.py <broker_list> <topic>"
+        print("Usage: direct_kafka_wordcount.py <broker_list> <topic>", file=sys.stderr)
         exit(-1)
 
     sc = SparkContext(appName="PythonStreamingDirectKafkaWordCount")

examples/src/main/python/streaming/flume_wordcount.py

@@ -23,8 +23,9 @@
  https://flume.apache.org/documentation.html
 
  and then run the example
-    `$ bin/spark-submit --jars external/flume-assembly/target/scala-*/\
-      spark-streaming-flume-assembly-*.jar examples/src/main/python/streaming/flume_wordcount.py \
+    `$ bin/spark-submit --jars \
+      external/flume-assembly/target/scala-*/spark-streaming-flume-assembly-*.jar \
+      examples/src/main/python/streaming/flume_wordcount.py \
       localhost 12345
 """
 from __future__ import print_function

examples/src/main/python/streaming/kafka_wordcount.py

@@ -23,8 +23,9 @@
  http://kafka.apache.org/documentation.html#quickstart
 
  and then run the example
-    `$ bin/spark-submit --jars external/kafka-assembly/target/scala-*/\
-      spark-streaming-kafka-assembly-*.jar examples/src/main/python/streaming/kafka_wordcount.py \
+    `$ bin/spark-submit --jars \
+      external/kafka-assembly/target/scala-*/spark-streaming-kafka-assembly-*.jar \
+      examples/src/main/python/streaming/kafka_wordcount.py \
       localhost:2181 test`
 """
 from __future__ import print_function

examples/src/main/python/streaming/mqtt_wordcount.py

@@ -26,8 +26,9 @@
  http://www.eclipse.org/paho/#getting-started
 
  and then run the example
-    `$ bin/spark-submit --jars external/mqtt-assembly/target/scala-*/\
-      spark-streaming-mqtt-assembly-*.jar examples/src/main/python/streaming/mqtt_wordcount.py \
+    `$ bin/spark-submit --jars \
+      external/mqtt-assembly/target/scala-*/spark-streaming-mqtt-assembly-*.jar \
+      examples/src/main/python/streaming/mqtt_wordcount.py \
       tcp://localhost:1883 foo`
 """
 

examples/src/main/python/streaming/queue_stream.py

@@ -36,8 +36,8 @@ if __name__ == "__main__":
     # Create the queue through which RDDs can be pushed to
     # a QueueInputDStream
     rddQueue = []
-    for i in xrange(5):
-        rddQueue += [ssc.sparkContext.parallelize([j for j in xrange(1, 1001)], 10)]
+    for i in range(5):
+        rddQueue += [ssc.sparkContext.parallelize([j for j in range(1, 1001)], 10)]
 
     # Create the QueueInputDStream and use it do some processing
     inputStream = ssc.queueStream(rddQueue)

python/pyspark/streaming/flume.py

@@ -31,7 +31,9 @@ __all__ = ['FlumeUtils', 'utf8_decoder']
 
 def utf8_decoder(s):
     """ Decode the unicode as UTF-8 """
-    return s and s.decode('utf-8')
+    if s is None:
+        return None
+    return s.decode('utf-8')
 
 
 class FlumeUtils(object):

python/pyspark/streaming/kafka.py

@@ -29,7 +29,9 @@ __all__ = ['Broker', 'KafkaUtils', 'OffsetRange', 'TopicAndPartition', 'utf8_dec
 
 def utf8_decoder(s):
     """ Decode the unicode as UTF-8 """
-    return s and s.decode('utf-8')
+    if s is None:
+        return None
+    return s.decode('utf-8')
 
 
 class KafkaUtils(object):

python/pyspark/streaming/kinesis.py

@@ -26,7 +26,9 @@ __all__ = ['KinesisUtils', 'InitialPositionInStream', 'utf8_decoder']
 
 def utf8_decoder(s):
     """ Decode the unicode as UTF-8 """
-    return s and s.decode('utf-8')
+    if s is None:
+        return None
+    return s.decode('utf-8')
 
 
 class KinesisUtils(object):