code: def conv(col, fromBase, toBase):
      
      sc = SparkContext._active_spark_context
      return Column(sc._jvm.functions.conv(_to_java_column(col), fromBase, toBase))
docs: Convert a number in a string column from one base to another.
  
      >>> df = spark.createDataFrame([("010101",)], ['n'])
      >>> df.select(conv(df.n, 2, 16).alias('hex')).collect()
      [Row(hex=u'15')]