def keras_dropout(layer, rate):
    '''keras dropout layer.
    '''

    from keras import layers

    input_dim = len(layer.input.shape)
    if input_dim == 2:
        return layers.SpatialDropout1D(rate)
    elif input_dim == 3:
        return layers.SpatialDropout2D(rate)
    elif input_dim == 4:
        return layers.SpatialDropout3D(rate)
    else:
        return layers.Dropout(rate)
keras dropout layer.