Also ...

You pass in ```self.added_gridmaps``` to ```_create_cf_grid_mapping()```, which is a reference to the list. The function may append a coordinate-system into this list as a result of its processing. So at that point the ```self.added_gridmaps``` is already updated.

There is no need to perform a ```return``` within ```_create_cf_grid_mapping()``` and assign the result back to ```self.added_gridmaps```.