Stacked Bar Chart with Centered Labels

I'm trying to "robustly" center the data labels in a stacked bar chart. A simple code example and the result are given below. As you can see, the data labels aren't really centered in all rectangles. What am I missing? ``` import numpy as np import matplotlib.pyplot as plt A = [45, 17, 47] B = [91, 70, 72] fig = plt.figure(facecolor="white") ax = fig.add_subplot(1, 1, 1) bar_width = 0.5 bar_l = np.arange(1, 4) tick_pos = [i + (bar_width / 2) for i in bar_l] ax1 = ax.bar(bar_l, A, width=bar_width, label="A", color="green") ax2 = ax.bar(bar_l, B, bottom=A, width=bar_width, label="B", color="blue") ax.set_ylabel("Count", fontsize=18) ax.set_xlabel("Class", fontsize=18) ax.legend(loc="best") plt.xticks(tick_pos, ["C1", "C2", "C3"], fontsize=16) plt.yticks(fontsize=16) for r1, r2 in zip(ax1, ax2): h1 = r1.get_height() h2 = r2.get_height() plt.text(r1.get_x() + r1.get_width() / 2., h1 / 2., "%d" % h1, ha="center", va="bottom", color="white", fontsize=16, fontweight="bold") plt.text(r2.get_x() + r2.get_width() / 2., h1 + h2 / 2., "%d" % h2, ha="center", va="bottom", color="white", fontsize=16, fontweight="bold") plt.show() ```