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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def getOrCreate(cls, conf=None):
 """ Get or instantiate a SparkContext and register it as a singleton object. :param conf: SparkConf (optional) """

        with SparkContext._lock:
            if SparkContext._active_spark_context is None:
                SparkContext(conf=conf or SparkConf())
            return SparkContext._active_spark_context