这是我的代码：
# map function
def echo(lines):
if lines:
for i, line in enumerate(lines):
print i, "=>", line
# load the data
idsFile = "ids.txt" # Should be some file on your system
linesData = sc.textFile(idsFile).cache()
# clean it
cleanLinesData = linesData.map(lambda line: line.strip())
filteredLinesData = cleanLinesData.filter(lambda line: True if line else False)
# setup task
answers = filteredLinesData.mapPartitions(echo, 2) # split file into 2 pieces
文件ids.txt：
1,2,3,4,5,1
6,4,8,3,2
9,9,9,9,9,9
100000000,1
10,10,10
1,2,4,2
要运行它，我运行：
$ IPYTHON=1 pyspark --master local[2]
然后我%cpaste代码（有没有更好的方法呢？）。
如果我只是尝试take()并看到值，我会得到合理的输出：
In[2]: filteredLinesData.take(6)
Out[2]:
[u'1,2,3,4,5,1',
u'6,4,8,3,2',
u'9,9,9,9,9,9',
u'100000000,1',
u'10,10,10',
u'1,2,4,2']
但是当我尝试实际执行setup mapPartitions()作业时，它失败了：
In [3]: executed = answers.collect()
14/09/12 11:18:22 INFO SparkContext: Starting job: collect at <ipython-input-3-6461aec48699>:1
14/09/12 11:18:22 INFO DAGScheduler: Got job 2 (collect at <ipython-input-3-6461aec48699>:1) with 2 output partitions (allowLocal=false)
14/09/12 11:18:22 INFO DAGScheduler: Final stage: Stage 2(collect at <ipython-input-3-6461aec48699>:1)
14/09/12 11:18:22 INFO DAGScheduler: Parents of final stage: List()
14/09/12 11:18:22 INFO DAGScheduler: Missing parents: List()
14/09/12 11:18:22 INFO DAGScheduler: Submitting Stage 2 (PythonRDD[3] at RDD at PythonRDD.scala:37), which has no missing parents
14/09/12 11:18:22 INFO DAGScheduler: Submitting 2 missing tasks from Stage 2 (PythonRDD[3] at RDD at PythonRDD.scala:37)
14/09/12 11:18:22 INFO TaskSchedulerImpl: Adding task set 2.0 with 2 tasks
14/09/12 11:18:22 INFO TaskSetManager: Starting task 2.0:0 as TID 0 on executor localhost: localhost (PROCESS_LOCAL)
14/09/12 11:18:22 INFO TaskSetManager: Serialized task 2.0:0 as 3112 bytes in 1 ms
14/09/12 11:18:22 INFO TaskSetManager: Starting task 2.0:1 as TID 1 on executor localhost: localhost (PROCESS_LOCAL)
14/09/12 11:18:22 INFO TaskSetManager: Serialized task 2.0:1 as 3112 bytes in 0 ms
14/09/12 11:18:22 INFO Executor: Running task ID 0
14/09/12 11:18:22 INFO Executor: Running task ID 1
14/09/12 11:18:22 INFO BlockManager: Found block broadcast_0 locally
14/09/12 11:18:22 INFO BlockManager: Found block broadcast_0 locally
14/09/12 11:18:22 INFO CacheManager: Partition rdd_1_1 not found, computing it
14/09/12 11:18:22 INFO CacheManager: Partition rdd_1_0 not found, computing it
14/09/12 11:18:22 INFO HadoopRDD: Input split: file:/Users/will/Code/spark/sumlines/ids.txt:31+32
14/09/12 11:18:22 INFO HadoopRDD: Input split: file:/Users/will/Code/spark/sumlines/ids.txt:0+31
14/09/12 11:18:22 INFO MemoryStore: ensureFreeSpace(288) called with curMem=133256, maxMem=308910489
14/09/12 11:18:22 INFO MemoryStore: Block rdd_1_1 stored as values to memory (estimated size 288.0 B, free 294.5 MB)
14/09/12 11:18:22 INFO MemoryStore: ensureFreeSpace(304) called with curMem=133544, maxMem=308910489
14/09/12 11:18:22 INFO MemoryStore: Block rdd_1_0 stored as values to memory (estimated size 304.0 B, free 294.5 MB)
14/09/12 11:18:22 INFO BlockManagerInfo: Added rdd_1_0 in memory on 18.111.61.9:58306 (size: 304.0 B, free: 294.6 MB)
14/09/12 11:18:22 INFO BlockManagerInfo: Added rdd_1_1 in memory on 18.111.61.9:58306 (size: 288.0 B, free: 294.6 MB)
14/09/12 11:18:22 INFO BlockManagerMaster: Updated info of block rdd_1_0
14/09/12 11:18:22 INFO BlockManagerMaster: Updated info of block rdd_1_1
0 => 1,2,3,4,5,1
1 => 6,4,8,3,2
2 => 9,9,9,9,9,9
0 => 100000000,1
1 => PySpark worker failed with exception:10,10,10
2 => 1,2,4,2
PySpark worker failed with exception:
Traceback (most recent call last):
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/worker.py", line 77, in main
serializer.dump_stream(func(split_index, iterator), outfile)
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 191, in dump_stream
self.serializer.dump_stream(self._batched(iterator), stream)
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 123, in dump_stream
for obj in iterator:
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 180, in _batched
for item in iterator:
TypeError: 'NoneType' object is not iterable
Traceback (most recent call last):
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/worker.py", line 77, in main
serializer.dump_stream(func(split_index, iterator), outfile)
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 191, in dump_stream
self.serializer.dump_stream(self._batched(iterator), stream)
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 123, in dump_stream
for obj in iterator:
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 180, in _batched
for item in iterator:
TypeError: 'NoneType' object is not iterable
14/09/12 11:18:22 ERROR Executor: Exception in task ID 1
org.apache.spark.api.python.PythonException: Traceback (most recent call last):
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/worker.py", line 77, in main
serializer.dump_stream(func(split_index, iterator), outfile)
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 191, in dump_stream
self.serializer.dump_stream(self._batched(iterator), stream)
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 123, in dump_stream
for obj in iterator:
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 180, in _batched
for item in iterator:
TypeError: 'NoneType' object is not iterable
at org.apache.spark.api.python.PythonRDD$$anon$1.read(PythonRDD.scala:115)
at org.apache.spark.api.python.PythonRDD$$anon$1.<init>(PythonRDD.scala:145)
at org.apache.spark.api.python.PythonRDD.compute(PythonRDD.scala:78)
at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:262)
at org.apache.spark.rdd.RDD.iterator(RDD.scala:229)
at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:111)
at org.apache.spark.scheduler.Task.run(Task.scala:51)
at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:187)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
14/09/12 11:18:22 ERROR Executor: Exception in task ID 0
org.apache.spark.api.python.PythonException: Traceback (most recent call last):
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/worker.py", line 77, in main
serializer.dump_stream(func(split_index, iterator), outfile)
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 191, in dump_stream
self.serializer.dump_stream(self._batched(iterator), stream)
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 123, in dump_stream
for obj in iterator:
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 180, in _batched
for item in iterator:
TypeError: 'NoneType' object is not iterable
at org.apache.spark.api.python.PythonRDD$$anon$1.read(PythonRDD.scala:115)
at org.apache.spark.api.python.PythonRDD$$anon$1.<init>(PythonRDD.scala:145)
at org.apache.spark.api.python.PythonRDD.compute(PythonRDD.scala:78)
at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:262)
at org.apache.spark.rdd.RDD.iterator(RDD.scala:229)
at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:111)
at org.apache.spark.scheduler.Task.run(Task.scala:51)
at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:187)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
14/09/12 11:18:22 WARN TaskSetManager: Lost TID 0 (task 2.0:0)
14/09/12 11:18:22 WARN TaskSetManager: Loss was due to org.apache.spark.api.python.PythonException
org.apache.spark.api.python.PythonException: Traceback (most recent call last):
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/worker.py", line 77, in main
serializer.dump_stream(func(split_index, iterator), outfile)
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 191, in dump_stream
self.serializer.dump_stream(self._batched(iterator), stream)
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 123, in dump_stream
for obj in iterator:
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 180, in _batched
for item in iterator:
TypeError: 'NoneType' object is not iterable
at org.apache.spark.api.python.PythonRDD$$anon$1.read(PythonRDD.scala:115)
at org.apache.spark.api.python.PythonRDD$$anon$1.<init>(PythonRDD.scala:145)
at org.apache.spark.api.python.PythonRDD.compute(PythonRDD.scala:78)
at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:262)
at org.apache.spark.rdd.RDD.iterator(RDD.scala:229)
at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:111)
at org.apache.spark.scheduler.Task.run(Task.scala:51)
at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:187)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
14/09/12 11:18:22 ERROR TaskSetManager: Task 2.0:0 failed 1 times; aborting job
14/09/12 11:18:22 INFO TaskSetManager: Loss was due to org.apache.spark.api.python.PythonException: Traceback (most recent call last):
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/worker.py", line 77, in main
serializer.dump_stream(func(split_index, iterator), outfile)
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 191, in dump_stream
self.serializer.dump_stream(self._batched(iterator), stream)
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 123, in dump_stream
for obj in iterator:
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 180, in _batched
for item in iterator:
TypeError: 'NoneType' object is not iterable
[duplicate 1]
14/09/12 11:18:22 INFO TaskSchedulerImpl: Removed TaskSet 2.0, whose tasks have all completed, from pool
14/09/12 11:18:22 INFO DAGScheduler: Failed to run collect at <ipython-input-3-6461aec48699>:1
14/09/12 11:18:22 INFO TaskSchedulerImpl: Cancelling stage 2
---------------------------------------------------------------------------
Py4JJavaError Traceback (most recent call last)
<ipython-input-3-6461aec48699> in <module>()
----> 1 executed = answers.collect()
/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/rdd.pyc in collect(self)
581 """
582 with _JavaStackTrace(self.context) as st:
--> 583 bytesInJava = self._jrdd.collect().iterator()
584 return list(self._collect_iterator_through_file(bytesInJava))
585
/usr/bin/spark-1.0.0-bin-hadoop2/python/lib/py4j-0.8.1-src.zip/py4j/java_gateway.py in __call__(self, *args)
535 answer = self.gateway_client.send_command(command)
536 return_value = get_return_value(answer, self.gateway_client,
--> 537 self.target_id, self.name)
538
539 for temp_arg in temp_args:
/usr/bin/spark-1.0.0-bin-hadoop2/python/lib/py4j-0.8.1-src.zip/py4j/protocol.py in get_return_value(answer, gateway_client, target_id, name)
298 raise Py4JJavaError(
299 'An error occurred while calling {0}{1}{2}.\n'.
--> 300 format(target_id, '.', name), value)
301 else:
302 raise Py4JError(
Py4JJavaError: An error occurred while calling o38.collect.
: org.apache.spark.SparkException: Job aborted due to stage failure: Task 2.0:0 failed 1 times, most recent failure: Exception failure in TID 0 on host localhost: org.apache.spark.api.python.PythonException: Traceback (most recent call last):
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/worker.py", line 77, in main
serializer.dump_stream(func(split_index, iterator), outfile)
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 191, in dump_stream
self.serializer.dump_stream(self._batched(iterator), stream)
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 123, in dump_stream
for obj in iterator:
File "/usr/bin/spark-1.0.0-bin-hadoop2/python/pyspark/serializers.py", line 180, in _batched
for item in iterator:
TypeError: 'NoneType' object is not iterable
org.apache.spark.api.python.PythonRDD$$anon$1.read(PythonRDD.scala:115)
org.apache.spark.api.python.PythonRDD$$anon$1.<init>(PythonRDD.scala:145)
org.apache.spark.api.python.PythonRDD.compute(PythonRDD.scala:78)
org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:262)
org.apache.spark.rdd.RDD.iterator(RDD.scala:229)
org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:111)
org.apache.spark.scheduler.Task.run(Task.scala:51)
org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:187)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
java.lang.Thread.run(Thread.java:745)
Driver stacktrace:
at org.apache.spark.scheduler.DAGScheduler.org$apache$spark$scheduler$DAGScheduler$$failJobAndIndependentStages(DAGScheduler.scala:1033)
at org.apache.spark.scheduler.DAGScheduler$$anonfun$abortStage$1.apply(DAGScheduler.scala:1017)
at org.apache.spark.scheduler.DAGScheduler$$anonfun$abortStage$1.apply(DAGScheduler.scala:1015)
at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:47)
at org.apache.spark.scheduler.DAGScheduler.abortStage(DAGScheduler.scala:1015)
at org.apache.spark.scheduler.DAGScheduler$$anonfun$handleTaskSetFailed$1.apply(DAGScheduler.scala:633)
at org.apache.spark.scheduler.DAGScheduler$$anonfun$handleTaskSetFailed$1.apply(DAGScheduler.scala:633)
at scala.Option.foreach(Option.scala:236)
at org.apache.spark.scheduler.DAGScheduler.handleTaskSetFailed(DAGScheduler.scala:633)
at org.apache.spark.scheduler.DAGSchedulerEventProcessActor$$anonfun$receive$2.applyOrElse(DAGScheduler.scala:1207)
at akka.actor.ActorCell.receiveMessage(ActorCell.scala:498)
at akka.actor.ActorCell.invoke(ActorCell.scala:456)
at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:237)
at akka.dispatch.Mailbox.run(Mailbox.scala:219)
at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:386)
at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)
显然对输入做了正确的事情，但由于某些原因，Spark最终会尝试向mapPartition()函数提供导致TypeError: 'NoneType' object is not iterable错误的函数。
任何想法我做错了什么？我完全不知所措。
答案 0 :(得分：6)
这里的问题是mapPartitions接受一个返回可迭代对象的函数，例如列表或生成器。您的echo函数会隐式返回None，这就是PySpark抱怨object NoneType is not iterable的原因。
正如Jonathan建议的那样，你可以使用foreachPartition这个函数（实际上是未经修改的）。我相信这将在local模式下运行PySpark时打印您的预期输出，但在集群上部署时可能不是您想要的：print语句的输出将打印在工人的日志，未显示在驱动程序上。
相反，我将echo功能修改为yield (i, "=>", line);现在，函数的返回类型应该是生成器。
答案 1 :(得分：5)
一些问题：
首先，要从ipython中运行脚本，您可以use execfile() or %run。
第二，mapPartitions doesn't take a number of partitions parameter;也许它确实在某个时候？您可以使用parallelize来显式设置分区数。
如果你这样运行，你会得到你想象的输出，但形式错误：
TypeError: 'NoneType' object is not iterable
那是因为mapPartition是一个转换;它期望一个函数将采用RDD的分区并返回RDD的新分区。您输出的是副作用，但没有返回新的RDD分区。也就是说，您正在寻找action，而不是转型。 foreach对每个元素采取行动; foreachPartition按分区工作，但需要一个返回None的生成器：
# map function
def echo(lines):
if lines:
for i, line in enumerate(lines):
print i, "=>", line
yield None
# load the data
idsFile = "ids.txt" # Should be some file on your system
linesData = sc.textFile(idsFile).cache()
# clean it
cleanLinesData = linesData.map(lambda line: line.strip())
filteredLinesData = cleanLinesData.filter(lambda line: True if line else False)
# setup task
answers = filteredLinesData.foreachPartition(echo)