def __init__(self, background_shape, background_filler=None):
        """
        Args:
            background_shape (tuple): shape of the background canvas.
            background_filler (BackgroundFiller): How to fill the background. Defaults to zero-filler.
        """
        if background_filler is None:
            background_filler = ConstantBackgroundFiller(0)

        self._init(locals())

        Args:
            background_shape (tuple): shape of the background canvas.
            background_filler (BackgroundFiller): How to fill the background. Defaults to zero-filler.
        
tensorpack/dataflow/imgaug/paste.py