i did
0.2 *  [xent_criterion(output, labels) for output in softmax_y] + \
[xent_criterion(output, labels) for output in softmax_y] 

the error is
[xent_criterion(output, labels) for output in softmax_y] + 
TypeError: can’t multiply sequence by non-int of type ‘float’
but i think that the problem is solved, i must do[ 0.2 * xent_criterion(output, labels) for output in softmax_y] + \
but still dont know how to learn the best valur of the weight, i just take 0.2 randomly