你能给我一段用python运行tff训练fashionmnist的代码案例吗

当然可以。以下是一段用python运行tff训练fashionmnist的代码案例：

import tensorflow as tf
import tensorflow_federated as tff

fashion_mnist = tf.keras.datasets.fashion_mnist
(x_train, y_train), (x_test, y_test) = fashion_mnist.load_data()

def preprocess(dataset):
    def batch_format_fn(element):
        return (tf.expand_dims(element['x'], axis=-1),
                tf.one_hot(element['y'], 10))
    return dataset.repeat(NUM_EPOCHS).shuffle(SHUFFLE_BUFFER).batch(
        BATCH_SIZE).map(batch_format_fn)

def make_federated_data(client_data, client_ids):
    return [preprocess(client_data.create_tf_dataset_for_client(x))
            for x in client_ids]

BATCH_SIZE = 100
NUM_EPOCHS = 10
SHUFFLE_BUFFER = 500
NUM_CLIENTS = 10

emnist_train, emnist_test = tff.simulation.datasets.emnist.load_data()

def create_compiled_keras_model():
    model = tf.keras.models.Sequential([
        tf.keras.layers.Conv2D(32, 5, padding='same', activation='relu'),
        tf.keras.layers.MaxPooling2D(),
        tf.keras.layers.Flatten(),
        tf.keras.layers.Dense(10, activation='softmax')
    ])
    model.compile(
        loss=tf.keras.losses.CategoricalCrossentropy(),
        optimizer=tf.keras.optimizers.SGD(learning_rate=0.02),
        metrics=[tf.keras.metrics.CategoricalAccuracy()])
    return model

# Wrap a Keras model for use with TFF.
def model_fn():
    keras_model = create_compiled_keras_model()
    return tff.learning.from_compiled_keras_model(keras_model, sample_batch)

train_data = make_federated_data(emnist_train, emnist_train.client_ids[:NUM_CLIENTS])

iterative_process = tff.learning.build_federated_averaging_process(
    model_fn,
    client_optimizer_fn=lambda: tf.keras.optimizers.SGD(learning_rate=0.02))

state = iterative_process.initialize()

for round_num in range(NUM_ROUNDS):
    state, metrics = iterative_process.next(state, train_data)
    print('round {:2d}, metrics={}'.format(round_num, metrics))

希望对您有所帮助。