spark 常见问题pyspark Cannot run multiple SparkContexts at once; existing SparkContext

在是使用 pyspark 连接spark 时出现一下错误，当时试了很多方都没有解决，最后终于解决。如下所示

from pyspark import SparkContext

from pyspark import SparkConf
import pyspark

string_test = 'pyspark_test'
print(pyspark.__version__)

conf = SparkConf().setAppName(string_test).setMaster('spark://master:7077')

sc = SparkContext(conf=conf)
#
list_test = [1, 2, 3]

x = sc.parallelize(list_test)

y = x.map(lambda x: (x, x * 2))

print (x.collect())

print (y.collect())

sc.stop()

报错

ValueError: Cannot run multiple SparkContexts at once; existing SparkContext(app=PySparkShell, master=local[*]) created by at /usr/local/spark/python/pyspark/shell.py:59 

解决办法
出现这个错误是因为之前已将启动了SparkContext ,所以需要先关闭spark，然后再启动