def _calc_concat_dim_coord(dim):
    if isinstance(dim, basestring):
        coord = None
    elif not hasattr(dim, 'dims'):
        # dim is not a DataArray or Coordinate
        dim_name = getattr(dim, 'name', None)
        if dim_name is None:
            dim_name = 'concat_dim'
        coord = Coordinate(dim_name, dim)
        dim = dim_name
    elif not hasattr(dim, 'name'):
        coord = as_variable(dim).to_coord()
        dim, = coord.dims
    else:
        coord = dim
        dim, = coord.dims
    return dim, coord
Instead of returning the default self, return a new instance of this
dataset/ETHPy150Open pydata/xarray/xarray/core/combine.py/_calc_concat_dim_coord--crossover with--dataset/ETHPy150Open twisted/nevow/nevow/_widget_plugin.py/WidgetPluginRoot.child_