def write_batch_norm_layer(model_name='sas', layer_name='bn', activation=
    'identity', src_layer='none'):
    """
    Generate Python code defining a SAS deep learning batch normalization layer

    Parameters
    ----------
    model_name : string, optional
       Name for deep learning model
    layer_name : string, optional
       Layer name
    activation : string, optional
       activation function
    src_layer : string, optional
       source layer(s) for the convolution layer

    Returns
    -------
    string

    """
    out = ['   s.addLayer(model=' + repr(model_name) + ', name=' + repr(
        layer_name) + ',', 
        '              layer=dict( type="batchnorm", act=' + repr(
        activation) + '),', '              srcLayers=' + src_layer + ')']
    return '\n'.join(out)
