Keras Multiply() layer in functional API

With keras > 2.0:

from keras.layers import multiply
output = multiply([dense_all, dense_att])

Under the functional API, you just use the multiply function, note the lowercase "m". The Multiply class is a layer as you see, intended to be used with the sequential API.

More information in https://keras.io/layers/merge/#multiply_1

You need to add one more open close parenthesis at front.

from keras.layers import Multiply
att_mull = Multiply()([dense_all, dense_att])