我在EMR上使用spark并编写了pyspark脚本，尝试执行时出现错误

from pyspark import SparkContext
sc = SparkContext()

这是错误

File "pyex.py", line 5, in <module>
    sc = SparkContext()   File "/usr/local/lib/python3.4/site-packages/pyspark/context.py", line 118, in __init__
    conf, jsc, profiler_cls)   File "/usr/local/lib/python3.4/site-packages/pyspark/context.py", line 195, in _do_init
    self._encryption_enabled = self._jvm.PythonUtils.getEncryptionEnabled(self._jsc)   File "/usr/local/lib/python3.4/site-packages/py4j/java_gateway.py", line 1487, in __getattr__
    "{0}.{1} does not exist in the JVM".format(self._fqn, name)) py4j.protocol.Py4JError: org.apache.spark.api.python.PythonUtils.getEncryptionEnabled does not exist in the JVM

我发现此答案说明我需要导入sparkcontext，但这也无法正常工作。