'Return *x* string formatted.  This function will use the attribute
self.fmt_xdata if it is callable, else will fall back on the xaxis
major formatter'

def format_xdata(self, x):

    try:
        return self.fmt_xdata(x)
    except TypeError:
        func = self.xaxis.get_major_formatter().format_data_short
        val = func(x)
        return val
