how to measure the accuracy of knn classifier in python

I have used knn to classify my dataset. But I do not know how to measure the accuracy of the trained classifier. Does scikit have any inbuilt function to check accuracy of knn classifier?

from sklearn.neighbors import KNeighborsClassifier
knn = KNeighborsClassifier()
knn.fit(training, train_label)    
predicted = knn.predict(testing)

Appreciate all the help. Thanks