The following code fails to run on Python 2.5.4:

from matplotlib import pylab as pl
import numpy as np

data = np.random.rand(6,6)
fig = pl.figure(1)
fig.clf()
ax = fig.add_subplot(1,1,1)
ax.imshow(data, interpolation='nearest', vmin=0.5, vmax=0.99)
pl.colorbar()

pl.show()

The error message is

C:\temp>python z.py
Traceback (most recent call last):
  File "z.py", line 10, in <module>
    pl.colorbar()
  File "C:\Python25\lib\site-packages\matplotlib\pyplot.py", line 1369, in colorbar
    ret = gcf().colorbar(mappable, cax = cax, ax=ax, **kw)
  File "C:\Python25\lib\site-packages\matplotlib\figure.py", line 1046, in colorbar
    cb = cbar.Colorbar(cax, mappable, **kw)
  File "C:\Python25\lib\site-packages\matplotlib\colorbar.py", line 622, in __init__
    mappable.autoscale_None() # Ensure mappable.norm.vmin, vmax
AttributeError: 'NoneType' object has no attribute 'autoscale_None'

How can I add colorbar to this code?

Following is the interpreter information:

Python 2.5.4 (r254:67916, Dec 23 2008, 15:10:54) [MSC v.1310 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>