matplotlib one data point with error bars

Question

How can I add asymmetric error bars to one data point using matplotlib python. Right now I have something like

x = 1

y = 2

yerr = 0.5

pl.errorbar(x, y, yerr=[yerr, 2*yerr],fmt='o')

but I get

In safezip, len(args[0])=1 but len(args[1])=2

Thanks!

(I tried the same plot line but with arrays for x and y and it works fine)

Answer 1

It is not very well documented, but errorbar() expects yerr to be a 2xN array if you want asymmetrical errorbars. For example:

import matplotlib.pyplot as plt

fig = plt.figure()
pl = fig.add_subplot(1, 1, 1)

x = 1
y = 2
yerr = 0.5
pl.errorbar(x, y, yerr=[[yerr], [2*yerr]],fmt='o')

plt.savefig('t.png')