def primary_keys_for(self, cls: ClassDefinition) -> List[SlotDefinitionName]:
return [slot_name for slot_name in self.all_slots_for(cls)<EOL>if self.schema.slots[slot_name].primary_key or self.schema.slots[slot_name].identifier]<EOL>
Return all primary keys / identifiers for cls

        @param cls: class to get keys for
        @return: List of primary keys