关于Python matplotlib的制图问题

为什么x,y坐标中的标签不会半透明呢，教程中的图片如图
但是实际的图片是这样的

为什么我的没有半透明的背景呢
代码如下：

#!python3
# coidng="utf-8"

import matplotlib.pyplot as plt
import numpy as np

if __name__ == "__main__":
        X = np.linspace(-np.pi, np.pi, 256, endpoint=True)
    S, Y = np.sin(X), X
    plt.figure(figsize=(10, 6), dpi=80)
    plt.subplot(111)
    plt.xlim(-np.pi * 1.1, np.pi * 1.1)
    plt.ylim(min(Y) * 1.1, max(Y) * 1.1)
    plt.xticks([-np.pi, -np.pi / 2, 0, np.pi / 2, np.pi],
               [r"$-\pi$", r"$-\pi/2$", r"$0$", r"$+\pi/2$", r"$+\pi$"])
    plt.yticks([-np.pi, -np.pi / 2, 0, np.pi / 2, np.pi],
               [r"$-\pi$", r"$-\pi/2$", r"$0$", r"$+\pi/2$", r"$+\pi$"])
    ax = plt.gca()
    ax.spines["top"].set_color("none")
    ax.spines["right"].set_color("none")
    ax.xaxis.set_ticks_position("bottom")
    ax.yaxis.set_ticks_position("left")
    ax.spines["bottom"].set_position(["data", 0])
    ax.spines["left"].set_position(["data", 0])
    for each in ax.get_xticklabels() + ax.get_yticklabels():
        each.set_fontsize(16)
        each.set_bbox(dict(facecolor="white", edgecolor="None", alpha=0.65))
    plt.plot(X, S, linewidth=2.5, color="blue", linestyle="-")
    plt.plot(X, Y, linewidth=2.5, color="red", linestyle="-")
    t = np.pi / 2
    plt.plot([t, t], [0, 1], linewidth=1.5, color="blue", linestyle="--")
    plt.plot([0, t], [1, 1], linewidth=1.5, color="blue", linestyle="--")
    plt.scatter([t, ], [1, ], 50, color="blue")
    plt.plot([-t, -t], [0, -t], linewidth=1.5, color="red", linestyle="--")
    plt.plot([0, -t], [-t, -t], linewidth=1.5, color="red", linestyle="--")
    plt.scatter([-t, ], [-t, ], 50, color="red")
    plt.annotate(r"$\sin(\frac{\pi}{2})=1$", xy=(t, 1), xycoords="data", xytext=(+10, +20),
                 textcoords="offset points", fontsize=16,
                 arrowprops=dict(arrowstyle="->", connectionstyle="arc3,rad=.2"))
    plt.annotate(r"$(\frac{-\pi}{2},\frac{-\pi}{2})$", xy=(-t, -t), xycoords="data", xytext=(+10, -20),
                 textcoords="offset points", fontsize=16,
                 arrowprops=dict(arrowstyle="->", connectionstyle="arc3,rad=.2"))
    plt.savefig(r'C:\Users\rengz\Desktop\exercice_7.png')
    plt.show()

附图

for label in ax.get_xticklabels() + ax.get_yticklabels():

label.set_fontsize(12)

# set zorder for ordering the plot in plt 2.0.2 or higher

label.set_bbox(dict(facecolor='white', edgecolor='none', alpha=0.8, zorder=2))

plt.show()

bbox设置目的内容的透明度相关参，facecolor调节 box 前景色，edgecolor 设置边框， 本处设置边框为无，alpha设置透明度.