code: def json_tuple(col, *fields):
      
      sc = SparkContext._active_spark_context
      jc = sc._jvm.functions.json_tuple(_to_java_column(col), _to_seq(sc, fields))
      return Column(jc)
docs: Creates a new row for a json column according to the given field names.
  
      :param col: string column in json format
      :param fields: list of fields to extract
  
      >>> data = [("1", '''{"f1": "value1", "f2": "value2"}'''), ("2", '''{"f1": "value12"}''')]
      >>> df = spark.createDataFrame(data, ("key", "jstring"))
      >>> df.select(df.key, json_tuple(df.jstring, 'f1', 'f2')).collect()
      [Row(key=u'1', c0=u'value1', c1=u'value2'), Row(key=u'2', c0=u'value12', c1=None)]