Save classifier to disk in scikit-learn

How do I save a trained Naive Bayes classifier to disk and use it to predict data?

I have the following sample program from the scikit-learn website:

from sklearn import datasets
iris = datasets.load_iris()
from sklearn.naive_bayes import GaussianNB
gnb = GaussianNB()
y_pred = gnb.fit(iris.data, iris.target).predict(iris.data)
print "Number of mislabeled points : %d" % (iris.target != y_pred).sum()