In general, in python code, you want to use duck typing and not `isinstance()`. So this is what I would do:
```python
from krux.util import hasmethod
if hasmethod(passed_regions, 'split'):
    # passed_regions is a string-like thing, split it.
    filters.extend([lambda r: r.name in passed_regions.split(',')])
else:
    # passed_regions better be a list-like thing.
    filters.extend([lambda r: r.name in passed_regions])
```