如何正确复制tf.keras.models.Model的自定义子类模型？

现存的复制限制 #

• 目前没有可以直接通用复制所有Keras模型的实现方案，内置的克隆操作仅能正常处理非tf.keras.models.Model子类化定义的模型。
• 直接使用copy.deepcopy()对模型实例执行复制操作时不会抛出即时报错，但后续只要尝试使用复制得到的模型实例，就会触发各类运行错误。
• 直接对继承自tf.keras.models.Model的自定义子类模型调用tf.keras.models.clone_model，会直接抛出类型校验错误。

可复现问题的示例代码 #

import tensorflow as tf

class MyModel(tf.keras.Model):

  def __init__(self):
    super(MyModel, self).__init__()
    self.dense1 = tf.keras.layers.Dense(4, activation=tf.nn.relu)
    self.dense2 = tf.keras.layers.Dense(5, activation=tf.nn.softmax)
    self.dropout = tf.keras.layers.Dropout(0.5)

  def call(self, inputs, training=False):
    x = self.dense1(inputs)
    if training:
      x = self.dropout(x, training=training)
    return self.dense2(x)


if __name__ == '__main__':
    model1 = MyModel()
    model2 = tf.keras.models.clone_model(model1)

运行触发的报错堆栈 #

Traceback (most recent call last):
  File "/Users/emadboctor/Library/Application Support/JetBrains/PyCharm2020.3/scratches/scratch.py", line 600, in <module>
    model2 = tf.keras.models.clone_model(model1)
  File "/usr/local/lib/python3.8/site-packages/tensorflow/python/keras/models.py", line 430, in clone_model
    return _clone_functional_model(
  File "/usr/local/lib/python3.8/site-packages/tensorflow/python/keras/models.py", line 171, in _clone_functional_model
    raise ValueError('Expected `model` argument '
ValueError: Expected `model` argument to be a functional `Model` instance, but got a subclass model instead.

内容的提问来源于stack exchange，提问作者watch-this