[GitHub] incubator-spark pull request: Added extra description on ValueErro...

[JoshRosen]

Github user JoshRosen commented on the pull request:

    https://github.com/apache/incubator-spark/pull/581#issuecomment-34797494
  
    I'd store the constructor's call site (filename + line number) as an 
instance variable inside SparkContext, since we already have the 
`SparkContext._active_spark_context` global to retrieve the running context.