ax = plt.subplot(111)
w = 0.3
ax.bar(x - w, y, width=w, color='b', align='center')
ax.bar(x, z, width=w, color='g', align='center')
ax.bar(x + w, k, width=w, color='r', align='center')
ax.xaxis_date()
ax.autoscale(tight=True)
plt.show()
python matplotlib multiple bars