I would go more with something like that.

```python
"""
save_path : str or None, optional
    Output filename for best model. At least one of save_path 
    or store_best_model should be defined. Defaults to None. 
store_best_model : bool, optional
    Stores best model in memory. At least one of save_path 
    or store_best_model should be defined. Defaults to False.
"""
```

And you raise an error if neither are defined.