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')]

def conv(col, fromBase, toBase):
    """
    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')]
    """
    sc = SparkContext._active_spark_context
    return Column(sc._jvm.functions.conv(_to_java_column(col), fromBase, toBase))