By supplying one argument, we can choose which index to swap the last
        index with. We can for example swap the first index with the last one as
        follows.

        >>> df.swaplevel(0)
                                            Grade
        January     History     Final exam      A
        February    Geography   Final exam      B
        March       History     Coursework      A
        April       Geography   Coursework      C

        We can also define explicitly which indices we want to swap by supplying values
        for both i and j. Here, we for example swap the first and second indices.

        >>> df.swaplevel(0, 1)
                                            Grade
        History     Final exam  January         A
        Geography   Final exam  February        B
        History     Coursework  March           A
        Geography   Coursework  April           C)