from sklearn import datasets
from sklearn.naive_bayes import GaussianNB

iris = datasets.load_iris()

gnb = GaussianNB()
y_pred = gnb.fit(iris.data, iris.target).predict(iris.data)

print("Number of mislabeled points out of a total %d points : %d" % (iris.data.shape[0],(iris.target != y_pred).sum()))

Number of mislabeled points out of a total 150 points : 6