如何使Matplotlib轴的HIGH/LOW标签自动居中于对应区域？

一、最简方案：用文本对齐参数直接搞定 #

你当前代码里的问题在于，axs.text()默认把文本的左下角作为锚点定位，所以即使选了25%/75%的坐标，文本也不会居中。只需要给text()加上ha='center'（水平居中）和va='center'（垂直居中）参数，就能让文本以设置的(x,y)为中心对齐，完美匹配你要的25%/75%位置效果，代码也不用改复杂。

修改标签部分的代码：

# y轴LOW/HIGH标签 - 垂直文本，水平居中到左侧偏移位置，垂直居中到25%/75%高度
axs.text(minx - 0.5 * offsetx, 0.25 * maxy, "LOW", fontdict={}, rotation="vertical",
         ha='center', va='center')
axs.text(minx - 0.5 * offsetx, 0.75 * maxy, "HIGH", fontdict={}, rotation="vertical",
         ha='center', va='center')

# x轴LOW/HIGH标签 - 水平文本，垂直居中到顶部偏移位置，水平居中到25%/75%宽度
axs.text(0.25 * maxx, maxy + 0.5 * offsety, "LOW", fontdict={},
         ha='center', va='center')
axs.text(0.75 * maxx, maxy + 0.5 * offsety, "HIGH", fontdict={},
         ha='center', va='center')

二、进阶：用Bbox实现包围盒精准居中 #

如果后续可能调整偏移量或图表范围，想让标签自动跟着包围盒走，可以用Bbox来定位，比如让标签完全居中在左侧竖条或顶部横条的对应区域：

from matplotlib.transforms import Bbox

# 定义左侧竖条的包围盒
left_bbox = Bbox.from_extents(minx - offsetx, miny, minx, maxy)
# y轴LOW标签：居中在左侧竖条下半部分
low_y = axs.text(0, 0, "LOW", rotation="vertical", ha='center', va='center')
low_y.set_position([left_bbox.x0 + left_bbox.width/2, left_bbox.y0 + left_bbox.height*0.25])

# y轴HIGH标签：居中在左侧竖条上半部分
high_y = axs.text(0, 0, "HIGH", rotation="vertical", ha='center', va='center')
high_y.set_position([left_bbox.x0 + left_bbox.width/2, left_bbox.y0 + left_bbox.height*0.75])

# 定义顶部横条的包围盒
top_bbox = Bbox.from_extents(minx, maxy, maxx, maxy + offsety)
# x轴LOW标签：居中在顶部横条左半部分
low_x = axs.text(0, 0, "LOW", ha='center', va='center')
low_x.set_position([top_bbox.x0 + top_bbox.width*0.25, top_bbox.y0 + top_bbox.height/2])

# x轴HIGH标签：居中在顶部横条右半部分
high_x = axs.text(0, 0, "HIGH", ha='center', va='center')
high_x.set_position([top_bbox.x0 + top_bbox.width*0.75, top_bbox.y0 + top_bbox.height/2])

这种方式的好处是，不管怎么调offsetx、offsety或者图表大小，标签都会自动保持在对应区域的中心，不用手动改坐标。

三、完整优化代码（含隐藏默认坐标轴） #

把最简方案整合进去，再加个隐藏默认坐标轴的操作，让图表更接近目标效果：

def create_my_plot():
    # initialize figure
    fig = Figure(figsize=(7, 6))
    axs = fig.subplots()
    minx, maxx, midx = 0, 1, 0.5
    miny, maxy, midy = 0, 1, 0.5
    offsetx, offsety = 0.15, 0.15
    axs.add_patch(mpatches.Rectangle((minx, maxy), maxx, offsety, fill=False, edgecolor="black", clip_on=False, lw=0.5))
    axs.add_patch(mpatches.Rectangle((minx, miny), -offsetx, maxy, fill=False, edgecolor="black", clip_on=False, lw=0.5))

    axs.add_patch(mpatches.Rectangle((minx, midy), midx, midy, alpha=0.1, facecolor="green"))
    axs.add_patch(mpatches.Rectangle((midx, midy), midx, midy, alpha=0.1, facecolor="yellow"))
    axs.add_patch(mpatches.Rectangle((minx, miny), midx, midy, alpha=0.1, facecolor="gray"))
    axs.add_patch(mpatches.Rectangle((midx, miny), midx, midy, alpha=0.1, facecolor="red"))

    axs.add_line(Line2D(xdata=(minx-offsetx, maxx), ydata=(midy, midy), clip_on=False, color="black", lw=0.5))
    axs.add_line(Line2D(xdata=(midx, midx), ydata=(miny, maxy + offsety), clip_on=False, color="black", lw=0.5))

    # 优化后的标签对齐
    axs.text(minx - 0.5 * offsetx, 0.25 * maxy, "LOW", fontdict={}, rotation="vertical",
             ha='center', va='center')
    axs.text(minx - 0.5 * offsetx, 0.75 * maxy, "HIGH", fontdict={}, rotation="vertical",
             ha='center', va='center')

    axs.text(0.25 * maxx, maxy + 0.5 * offsety, "LOW", fontdict={},
             ha='center', va='center')
    axs.text(0.75 * maxx, maxy + 0.5 * offsety, "HIGH", fontdict={},
             ha='center', va='center')

    # 隐藏默认坐标轴，让图表更干净
    axs.set_xlim(minx - offsetx, maxx)
    axs.set_ylim(miny, maxy + offsety)
    axs.set_xticks([])
    axs.set_yticks([])
    for spine in axs.spines.values():
        spine.set_visible(False)

    buf = BytesIO()
    fig.savefig(buf, format="png")
    data = base64.b64encode(buf.getbuffer()).decode("ascii")

    return f"<img src='data:image/png;base64,{data}'/>"

内容的提问来源于stack exchange，提问作者Tarquinius