iris_classifier.py

from sklearn import datasets

iris = datasets.load_iris()

X = iris.data
y = iris.target

from sklearn.model_selection import train_test_split
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.25)

from sklearn import tree
classifier = tree.DecisionTreeClassifier()

classifier.fit(X_train, y_train)

predictions = classifier.predict(X_test)

from sklearn.metrics import accuracy_score
print(accuracy_score(y_test, predictions))