如何将tf.estimator转换为keras模型？

import tensorflow as tf
from tensorflow import keras

estimator = tf.estimator.Estimator(model_fn=model_fn, model_dir=model_dir)

keras_model = keras.models.Sequential()

def copy_weights_to_keras_model(estimator, keras_model):
    for layer in keras_model.layers:
        if layer.weights:
            weights = []
            for weight in layer.weights:
                weights.append(estimator.get_variable_value(weight.name))
            layer.set_weights(weights)

copy_weights_to_keras_model(estimator, keras_model)