code: def date_format(date, format):
      
      sc = SparkContext._active_spark_context
      return Column(sc._jvm.functions.date_format(_to_java_column(date), format))
docs: Converts a date/timestamp/string to a value of string in the format specified by the date
      format given by the second argument.
  
      A pattern could be for instance `dd.MM.yyyy` and could return a string like '18.03.1993'. All
      pattern letters of the Java class `java.time.format.DateTimeFormatter` can be used.
  
      .. note:: Use when ever possible specialized functions like `year`. These benefit from a
          specialized implementation.
  
      >>> df = spark.createDataFrame([('2015-04-08',)], ['dt'])
      >>> df.select(date_format('dt', 'MM/dd/yyy').alias('date')).collect()
      [Row(date=u'04/08/2015')]