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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def create_reward_encoder():
 """Creates TF ops to track and increment recent average cumulative reward."""

        last_reward = tf.Variable(0, name="last_reward", trainable=False, dtype=tf.float32)
        new_reward = tf.placeholder(shape=[], dtype=tf.float32, name='new_reward')
        update_reward = tf.assign(last_reward, new_reward)
        return last_reward, new_reward, update_reward