python画图如何在标题中调用变量

语法是：

y=L_B z='L_B' plt.plot(y, '-p', color='grey', marker = 'o', markersize=1, linewidth=1, markerfacecolor='red', markeredgecolor='grey', markeredgewidth=1) plt.ylim(min(y), max(y)) plt.title(**'{}'.format(z)**, fontsize=18)