def import_lookup_class(lookup_class):
    """
    Import lookup_class as a dotted base and ensure it extends LookupBase
    """
    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
Import lookup_class as a dotted base and ensure it extends LookupBase