
    Set the *y* axis label of the current axis.

    Defaults override is::

        override = {
           'fontsize'            : 'small',
           'verticalalignment'   : 'center',
           'horizontalalignment' : 'right',
           'rotation'='vertical' : }

    .. seealso::

        :func:`~matplotlib.pyplot.text`
            For information on how override and the optional args
            work.
    