code: def add_months(start, months):
      
      sc = SparkContext._active_spark_context
      return Column(sc._jvm.functions.add_months(_to_java_column(start), months))
docs: Returns the date that is `months` months after `start`
  
      >>> df = spark.createDataFrame([('2015-04-08',)], ['dt'])
      >>> df.select(add_months(df.dt, 1).alias('next_month')).collect()
      [Row(next_month=datetime.date(2015, 5, 8))]