Decorated topographies cannot be translated

[sannant]

    def __init__(self, topography, offset=(0, 0), info={}):
        """
        Keyword Arguments:
        topography  -- SurfaceTopography to translate
        offset -- Translation offset in number of grid points
        """
        super().__init__(topography, info=info)
>       assert isinstance(topography, Topography)
E       AssertionError