code: def import_lookup_class(lookup_class):
      
      from selectable.base import LookupBase
      if isinstance(lookup_class, string_types):
          mod_str, cls_str = lookup_class.rsplit('.', 1)
          mod = import_module(mod_str)
          lookup_class = getattr(mod, cls_str)
      if not issubclass(lookup_class, LookupBase):
          raise TypeError('lookup_class must extend from selectable.base.LookupBase')
      return lookup_class
docs: Import lookup_class as a dotted base and ensure it extends LookupBase