'Return *z* string formatted.  This function will use the
:attr:`fmt_zdata` attribute if it is callable, else will fall
back on the zaxis major formatter'

def format_zdata(self, z):

    try:
        return self.fmt_zdata(z)
    except (AttributeError, TypeError):
        func = self.zaxis.get_major_formatter().format_data_short
        val = func(z)
        return val
