from sklearn import datasets
from sklearn.cross_validation import train_test_split
from sklearn.naive_bayes import GaussianNB

digits = datasets.load_digits()

train_X, test_X, train_y, test_y = train_test_split(digits.data, digits.target, test_size=0.33)

nb_estimator = GaussianNB()
nb_estimator.fit(train_X, train_y)
nb_estimator.score(test_X, test_y)

from sklearn import cross_validation

cross_validation.cross_val_score(nb_estimator, test_X, test_y, cv=6)