tl;dr 为避免这种情况，请将您的输入转换为 float32

X = tf.cast(iris[:, :3], tf.float32)y = tf.cast(iris[:, 3], tf.float32)

或使用 numpy:

X = np.array(iris[:, :3], dtype=np.float32)y = np.array(iris[:, 3], dtype=np.float32)

说明

默认情况下，Tensorflow 使用 floatx，默认为 float32，这是深度学习的标准.您可以验证这一点:

 将 tensorflow 导入为 tftf.keras.backend.floatx()

输出[3]:'float32'

您提供的输入(Iris 数据集)是 dtype float64，因此 Tensorflow 的默认权重 dtype 与输入之间存在不匹配.Tensorflow 不喜欢那样，因为转换(更改 dtype)成本很高.Tensorflow 在操作不同 dtype 的张量时通常会抛出错误(例如，比较 float32 logits 和 float64 标签).

新行为"它在谈论:

层 my_model_1 将输入张量从 dtype float64 转换为层的 dtype 为 float32，这是 TensorFlow 2 中的新行为

是它会自动将输入的数据类型转换为 float32.在这种情况下，Tensorflow 1.X 可能会抛出异常，尽管我不能说我曾经使用过它.

Before my Tensorflow neural network starts training, the following warning prints out:

WARNING:tensorflow:Layer my_model is casting an input tensor from dtype float64 to the layer's dtype of float32, which is new behavior in TensorFlow 2. The layer has dtype float32 because it's dtype defaults to floatx. If you intended to run this layer in float32, you can safely ignore this warning.

If in doubt, this warning is likely only an issue if you are porting a TensorFlow 1.X model to TensorFlow 2. To change all layers to have dtype float64 by default, call tf.keras.backend.set_floatx('float64').

To change just this layer, pass dtype='float64' to the layer constructor. If you are the author of this layer, you can disable autocasting by passing autocast=False to the base Layer constructor.

Now, based on the error message, I am able to silence this error message by setting the backend to 'float64'. But, I would like to get to the bottom of this and set the right dtypes manually.

Full code:

import tensorflow as tf
from tensorflow.keras.layers import Dense, Concatenate
from tensorflow.keras import Model
from sklearn.datasets import load_iris
iris, target = load_iris(return_X_y=True)

X = iris[:, :3]
y = iris[:, 3]

ds = tf.data.Dataset.from_tensor_slices((X, y)).shuffle(25).batch(8)

class MyModel(Model):
  def __init__(self):
    super(MyModel, self).__init__()
    self.d0 = Dense(16, activation='relu')
    self.d1 = Dense(32, activation='relu')
    self.d2 = Dense(1, activation='linear')

  def call(self, x):
    x = self.d0(x)
    x = self.d1(x)
    x = self.d2(x)
    return x

model = MyModel()

loss_object = tf.keras.losses.MeanSquaredError()

optimizer = tf.keras.optimizers.Adam(learning_rate=5e-4)

loss = tf.keras.metrics.Mean(name='loss')
error = tf.keras.metrics.MeanSquaredError()

@tf.function
def train_step(inputs, targets):
    with tf.GradientTape() as tape:
        predictions = model(inputs)
        run_loss = loss_object(targets, predictions)
    gradients = tape.gradient(run_loss, model.trainable_variables)
    optimizer.apply_gradients(zip(gradients, model.trainable_variables))
    loss(run_loss)
    error(predictions, targets)

for epoch in range(10):
  for data, labels in ds:
    train_step(data, labels)

  template = 'Epoch {:>2}, Loss: {:>7.4f}, MSE: {:>6.2f}'
  print(template.format(epoch+1,
                        loss.result(),
                        error.result()*100))
  # Reset the metrics for the next epoch
  loss.reset_states()
  error.reset_states()

tl;dr to avoid this, cast your input to float32

X = tf.cast(iris[:, :3], tf.float32) 
y = tf.cast(iris[:, 3], tf.float32)

or with numpy:

X = np.array(iris[:, :3], dtype=np.float32)
y = np.array(iris[:, 3], dtype=np.float32)

Explanation

By default, Tensorflow uses floatx, which defaults to float32, which is standard for deep learning. You can verify this:

import tensorflow as tf
tf.keras.backend.floatx()

Out[3]: 'float32'

The input you provided (the Iris dataset), is of dtype float64, so there is a mismatch between Tensorflow's default dtype for weights, and the input. Tensorflow doesn't like that, because casting (changing the dtype) is costly. Tensorflow will generally throw an error when manipulating tensors of different dtypes (e.g., comparing float32 logits and float64 labels).

The "new behavior" it's talking about:

Layer my_model_1 is casting an input tensor from dtype float64 to the layer's dtype of float32, which is new behavior in TensorFlow 2

Is that it will automatically cast the input dtype to float32. Tensorflow 1.X probably threw an exception in this situation, although I can't say I've ever used it.