Compatibility for data_based_init

- also ensure that only trainable weights are updated

keras/weightnorm.py

@@ -192,9 +192,11 @@ def data_based_init(model, input):
     # get all layer name, output, weight, bias tuples
     layer_output_weight_bias = []
     for l in model.layers:
-        if hasattr(l, 'W') and hasattr(l, 'b'):
+        trainable_weights = l.trainable_weights
+        if len(trainable_weights) == 2:
+            W,b = trainable_weights
             assert(l.built)
-            layer_output_weight_bias.append( (l.name,l.get_output_at(0),l.W,l.b) ) # if more than one node, only use the first
+            layer_output_weight_bias.append((l.name,l.get_output_at(0),W,b)) # if more than one node, only use the first
 
     # iterate over our list and do data dependent init
     sess = K.get_session()