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')]

def lpad(col, len, pad):
    """
    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')]
    """
    sc = SparkContext._active_spark_context
    return Column(sc._jvm.functions.lpad(_to_java_column(col), len, pad))