Parses the expression string into the column that it represents

    >>> df.select(expr("length(name)")).collect()
    [Row(length(name)=5), Row(length(name)=3)]

def expr(str):
    """Parses the expression string into the column that it represents

    >>> df.select(expr("length(name)")).collect()
    [Row(length(name)=5), Row(length(name)=3)]
    """
    sc = SparkContext._active_spark_context
    return Column(sc._jvm.functions.expr(str))