Plots the current state of the shell's independent vs. dependent variables on the
        same set of axes. Give filename to save to as argument or leave blank to show.

def do_plot(self, arg):
        """Plots the current state of the shell's independent vs. dependent variables on the
        same set of axes. Give filename to save to as argument or leave blank to show.
        """
        usable, filename, append = self._redirect_split(arg)
        self.curargs["xscale"] = None
        self.curargs["yscale"] = None
        self._plot_generic(filename)