Unset trainable attributes for parameters in lasagne / nolearn neural networks

Question

I'm implementing a convolutional neural network using lasagne nolearn.

I'd like to fix some parameters that prelearned. How can I set some layers untrainable?

Actually, though I removed 'trainable' attribute of some layers, the number shown in the layer information before fitting, namely, such as

Neural Network with *** learnable parameters never change.

Besides, I'm afraid that the greeting function in 'handers.py'

def _get_greeting(nn):
    shapes = [param.get_value().shape for param in
              nn.get_all_params() if param]

should be

nn.get_all_params(trainable=True) if param]

but I'm not sure how it affect on training.