<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def log(arg1, arg2=None):
 """Returns the first argument-based logarithm of the second argument. If there is only one argument, then this takes the natural logarithm of the argument. ['0.30102', '0.69897'] ['0.69314', '1.60943'] """

    sc = SparkContext._active_spark_context
    if arg2 is None:
        jc = sc._jvm.functions.log(_to_java_column(arg1))
    else:
        jc = sc._jvm.functions.log(arg1, _to_java_column(arg2))
    return Column(jc)