code: def lpad(col, len, pad):
      
      sc = SparkContext._active_spark_context
      return Column(sc._jvm.functions.lpad(_to_java_column(col), len, pad))
docs: Left-pad the string column to width `len` with `pad`.
  
      >>> df = spark.createDataFrame([('abcd',)], ['s',])
      >>> df.select(lpad(df.s, 6, '#').alias('s')).collect()
      [Row(s=u'##abcd')]