Neural network with fixed weights in Python lasagne
I'm not sure what your intention is by setting the weights to zero. Have you looked at dropout layers?

l_hid1 = lasagne.layers.DenseLayer(num_units=200)

l_hid1_drop = lasagne.layers.DropoutLayer(l_hid1, p=0.5)


This should drop 50% of your data from the l_hid1 layer.