Typerror in machine learning tutorial, numpy

This is the notebook that's giving me a problem: https://github.com/justmarkham/scikit-learn-videos/blob/master/07_cross_validation.ipynb

from sklearn.cross_validation import KFold
kf = KFold(25, n_folds=5, shuffle=False)

# print the contents of each training and testing set
print('{} {:^61} {}'.format('Iteration', 'Training set observations',             
'Testing set observations'))
for iteration, data in enumerate(kf, start=1):
    print('{:^9} {} {:^25}'.format(iteration, data[0], data[1]))

This is the error I get:

TypeError: unsupported format string passed to numpy.ndarray.__format__

I don't really know where to start because I'm not that familiar with numpy.