from matplotlib import pyplot as plt
import numpy as np

# bar 柱状图
n = 8
X = np.arange(n)
Y1 = (1 - X/float(n))*np.random.uniform(0.5, 1.0, n)
Y2 = (1 - X/float(n))*np.random.uniform(0.5, 1.0, n)
plt.bar(X, +Y1, facecolor="steelblue", edgecolor="red")
plt.bar(X, -Y2, facecolor="#9999ff", edgecolor="red")
# 给柱状图加上标注
for x, y in zip(X, Y1):
    # ha horizontal alignment 左右对齐；va 上下对齐
    plt.text(x, y+0.05, "%.2f" % y, ha="center", va="bottom")



plt.xlim((-1, 13))
plt.ylim((-1.25, 1.25))
plt.xticks(())
plt.yticks(())
plt.show()