For the Lambda, it’s imported in the import section, so I thought I might be able to use it. There’s one line giving hint:

“* Recall that if you were implementing in numpy instead of Keras, you would extract a slice from a 3D numpy array like this:”

In this case, I need to take a slice that’s feed in as input X = Input(shape=(Tx, n_values), name="INPUT"), at particular time t. Checking on Lambda and example, I thought the construct Lambda(lambda x: x[:, t, :], name="Slice_"+str(t))(X) would do "Step 2.A: select the “t"th time step vector from X”.

I think I understand that I need to extract a 2D slice from a 3D input tensor, but I’m sure how.