
        >>> df.xs('cat', level=1)
                           num_legs  num_wings
        class  locomotion
        mammal walks              4          0

        Get values at several indexes and levels

        >>> df.xs(('bird', 'walks'),
        ...       level=[0, 'locomotion'])
                 num_legs  num_wings
        animal
        penguin         2          2

        Get values at specified column and axis

        >>> df.xs('num_wings', axis=1)
        class   animal   locomotion
        mammal  cat      walks         0
                dog      walks         0
                bat      flies         2
        bird    penguin  walks         2
        Name: num_wings, dtype: int64
        z7list keys are not supported in xs, pass a tuple insteadNz