controlliing a fill pattern in matplotlib
import pandas as pd
import numpy as np
n = 8
a = np.random.random(n)
b = np.random.random(n)
x = np.arange(n)
plt.bar(x,a, color='w', hatch='x')
plt.bar(x,a+b, bottom = a, color = 'w', hatch = '/')
plt.show()