Plot simple errorbar using pyplot

gistfile1.txt

import numpy as np
import matplotlib.pyplot as plt

# example data
x = np.arange(0.5, 5.5, 0.5)
print x

y = np.exp(-x)
print y

yerr = np.zeros(x.shape) + 0.2
yerr[[3, 6]] = 0.3
print yerr

plt.errorbar(x, y + 2.1, yerr=yerr)
plt.show()