import pickle


def init(pa):
    """
    Load the pickled model back into memory. Since loading models can be
    expensive, this function is cached so that the model only needs to be loaded
    into memory once.

    Returns:
        model (sklearn.tree.DecisionTreeClassifier): The trained decision tree.
    """
    with open(pa.model_artifact('model.pkl'), 'rb') as stream:
        return pickle.load(stream)