Creates a :class:`WindowSpec` with the partitioning defined.

def partitionBy(*cols):
        """
        Creates a :class:`WindowSpec` with the partitioning defined.
        """
        sc = SparkContext._active_spark_context
        jspec = sc._jvm.org.apache.spark.sql.expressions.Window.partitionBy(_to_java_cols(cols))
        return WindowSpec(jspec)