Calculating NBAccuracy

def NBAccuracy(features_train, labels_train, features_test, labels_test):

	from sklearn.naive_bayes import GaussianNB
	clf = GaussianNB()
	pref = clf.predict(features_test)
	accuracy =
	return accuracy

from class_vis import prettyPicture
from prep_terrain_data import makeTerrainData
from classify import NBAccuracy

import matplotlib.pyplot as plt
import numpy as np
import pylab as pl

features_train, labels_train, features_test, labels_test = makeTerrainData()

def submitAccuracy():
	accuracy = NBAccuracy(features_train, labels_train, features_test, labels_test)
	return accuracy