x = [datetime.datetime(2010, 12, 1, 10, 0), datetime.datetime(2011, 1, 4, 9,
    0), datetime.datetime(2011, 5, 5, 9, 0)]
y = [4, 9, 2]
ax = plt.subplot(111)
ax.bar(x, y, width=10)
ax.xaxis_date()
plt.show()
matplotlib bar chart with dates