我在lablepointRDD的時候，都會出現錯誤，可是我明明是按照書<python+spark2.0+Hadoop機器學習與大數據分析實戰>上的code打，想詢問大大能不能幫我看一下，小的感激不盡！！！！！！

使用環境
OS: linux ubuntu 14.04
language: python 2 + spark 2.0

＃讀取檔案
if sc.master[0:5] == "local":
    Path = "file:/home/hduser/pythonwork/PythonProject/"
else:
    Path = "hdfs://master:9000/user/hduser/"

print(" Load  Data... ")
rawDataWithHeader = sc.textFile(Path+"data/train.csv")
header = rawDataWithHeader.first()
rawData = rawDataWithHeader.filter(lambda x:x != header)
rData = rawData.map(lambda x: x.replace("\"",""))
lines = rData.map(lambda x: x.split(","))
print("共計：" + str(lines.count()) + "筆")

# 擷取數值欄位
import numpy as np
def extract_feature(record,featureEnd):
    numericalFeatures = [covert_float(field) for field in record [0:featureEnd]]
    return numericalFeatures

def convert_float(x):
    return (0 if x=="?" else float(x))
    
# 擷取lable欄位
def extract_label(record):
    label = (record[-1])
    return float(label)-1

# Spark LabelpointRDD
from pyspark.mllib.regression import LabeledPoint
labelpointRDD = lines.map(lambda r: LabeledPoint (
            extract_label(r),
            extract_feature(r,len(r)-1)))

# Error 到這邊出現錯誤
labelpointRDD.first()

錯誤資訊如下

Py4JJavaError: An error occurred while calling z:org.apache.spark.api.python.PythonRDD.runJob.
: org.apache.spark.SparkException: Job aborted due to stage failure: Task 0 in stage 27.0 failed 1 times, most recent failure: Lost task 0.0 in stage 27.0 (TID 27, localhost): org.apache.spark.api.python.PythonException: Traceback (most recent call last):
  File "/usr/local/spark/python/lib/pyspark.zip/pyspark/worker.py", line 172, in main
    process()
  File "/usr/local/spark/python/lib/pyspark.zip/pyspark/worker.py", line 167, in process
    serializer.dump_stream(func(split_index, iterator), outfile)
  File "/usr/local/spark/python/lib/pyspark.zip/pyspark/serializers.py", line 263, in dump_stream
    vs = list(itertools.islice(iterator, batch))
  File "/usr/local/spark/python/pyspark/rdd.py", line 1306, in takeUpToNumLeft
    yield next(iterator)
  File "<ipython-input-58-1c4bc0cb5b26>", line 7, in <lambda>
  File "<ipython-input-42-f603c8aa108c>", line 4, in extract_feature
  
NameError: global name 'covert_float' is not defined
	at org.apache.spark.api.python.PythonRunner$$anon$1.read(PythonRDD.scala:193)
	at org.apache.spark.api.python.PythonRunner$$anon$1.<init>(PythonRDD.scala:234)
	at org.apache.spark.api.python.PythonRunner.compute(PythonRDD.scala:152)
	at org.apache.spark.api.python.PythonRDD.compute(PythonRDD.scala:63)
	at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:319)
	at org.apache.spark.rdd.RDD.iterator(RDD.scala:283)
	at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:70)
	at org.apache.spark.scheduler.Task.run(Task.scala:85)
	at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:274)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1152)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:622)
	at java.lang.Thread.run(Thread.java:748)

Driver stacktrace:
	at org.apache.spark.scheduler.DAGScheduler.org$apache$spark$scheduler$DAGScheduler$$failJobAndIndependentStages(DAGScheduler.scala:1450)
 at org.apache.spark.scheduler.DAGScheduler$$anonfun$abortStage$1.apply(DAGScheduler.scala:1438)
	at org.apache.spark.scheduler.DAGScheduler$$anonfun$abortStage$1.apply(DAGScheduler.scala:1437)
	at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
	at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
	at org.apache.spark.scheduler.DAGScheduler.abortStage(DAGScheduler.scala:1437)
	at org.apache.spark.scheduler.DAGScheduler$$anonfun$handleTaskSetFailed$1.apply(DAGScheduler.scala:811)
	at org.apache.spark.scheduler.DAGScheduler$$anonfun$handleTaskSetFailed$1.apply(DAGScheduler.scala:811)
	at scala.Option.foreach(Option.scala:257)
	at org.apache.spark.scheduler.DAGScheduler.handleTaskSetFailed(DAGScheduler.scala:811)
	at org.apache.spark.scheduler.DAGSchedulerEventProcessLoop.doOnReceive(DAGScheduler.scala:1659)
	at org.apache.spark.scheduler.DAGSchedulerEventProcessLoop.onReceive(DAGScheduler.scala:1618)
	at org.apache.spark.scheduler.DAGSchedulerEventProcessLoop.onReceive(DAGScheduler.scala:1607)
	at org.apache.spark.util.EventLoop$$anon$1.run(EventLoop.scala:48)
	at org.apache.spark.scheduler.DAGScheduler.runJob(DAGScheduler.scala:632)
	at org.apache.spark.SparkContext.runJob(SparkContext.scala:1871)
	at org.apache.spark.SparkContext.runJob(SparkContext.scala:1884)
	at org.apache.spark.SparkContext.runJob(SparkContext.scala:1897)
	at org.apache.spark.api.python.PythonRDD$.runJob(PythonRDD.scala:441)
	at org.apache.spark.api.python.PythonRDD.runJob(PythonRDD.scala)
	at sun.reflect.GeneratedMethodAccessor36.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:237)
	at py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:357)
	at py4j.Gateway.invoke(Gateway.java:280)
	at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:128)
	at py4j.commands.CallCommand.execute(CallCommand.java:79)
	at py4j.GatewayConnection.run(GatewayConnection.java:211)
	at java.lang.Thread.run(Thread.java:748)
Caused by: org.apache.spark.api.python.PythonException: Traceback (most recent call last):
  File "/usr/local/spark/python/lib/pyspark.zip/pyspark/worker.py", line 172, in main
    process()
  File "/usr/local/spark/python/lib/pyspark.zip/pyspark/worker.py", line 167, in process
    serializer.dump_stream(func(split_index, iterator), outfile)
  File "/usr/local/spark/python/lib/pyspark.zip/pyspark/serializers.py", line 263, in dump_stream
    vs = list(itertools.islice(iterator, batch))
  File "/usr/local/spark/python/pyspark/rdd.py", line 1306, in takeUpToNumLeft
    yield next(iterator)
  File "<ipython-input-58-1c4bc0cb5b26>", line 7, in <lambda>
  File "<ipython-input-42-f603c8aa108c>", line 4, in extract_feature
NameError: global name 'covert_float' is not defined
	at org.apache.spark.api.python.PythonRunner$$anon$1.read(PythonRDD.scala:193)
	at org.apache.spark.api.python.PythonRunner$$anon$1.<init>(PythonRDD.scala:234)
	at org.apache.spark.api.python.PythonRunner.compute(PythonRDD.scala:152)
	at org.apache.spark.api.python.PythonRDD.compute(PythonRDD.scala:63)
	at org.apache.spark.rdd.RDD.computeOrReadCheckpoint(RDD.scala:319)
    at org.apache.spark.rdd.RDD.iterator(RDD.scala:283)
	at org.apache.spark.scheduler.ResultTask.runTask(ResultTask.scala:70)
	at org.apache.spark.scheduler.Task.run(Task.scala:85)
	at org.apache.spark.executor.Executor$TaskRunner.run(Executor.scala:274)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1152)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:622)
	... 1 more

拜託大家！感謝大家！！