'Return y string formatted.  This function will use the
:attr:`fmt_ydata` attribute if it is callable, else will fall
back on the yaxis major formatter'

def format_ydata(self, y):

    try:
        return self.fmt_ydata(y)
    except TypeError:
        func = self.yaxis.get_major_formatter().format_data_short
        val = func(y)
        return val
