code: def stats(self):
          
          assert self.backend.LOAD_count >= 0, "LOAD_count < 0"
          assert self.backend.LOAD_byte >= 0, "LOAD_byte < 0"
          assert self.backend.STORE_count >= 0, "STORE_count < 0"
          assert self.backend.STORE_byte >= 0, "STORE_byte < 0"
          assert self.backend.HIT_count >= 0, "HIT_count < 0"
          assert self.backend.HIT_byte >= 0, "HIT_byte < 0"
          assert self.backend.MISS_count >= 0, "MISS_count < 0"
          assert self.backend.MISS_byte >= 0, "MISS_byte < 0"
          assert self.backend.EVICT_count >= 0, "EVICT_count < 0"
          assert self.backend.EVICT_byte >= 0, "EVICT_byte < 0"
          return {'name': self.name,
                  'LOAD_count': self.backend.LOAD_count,
                  'LOAD_byte': self.backend.LOAD_byte,
                  'STORE_count': self.backend.STORE_count,
                  'STORE_byte': self.backend.STORE_byte,
                  'HIT_count': self.backend.HIT_count,
                  'HIT_byte': self.backend.HIT_byte,
                  'MISS_count': self.backend.MISS_count,
                  'MISS_byte': self.backend.MISS_byte,
                  'EVICT_count': self.backend.EVICT_count,
                  'EVICT_byte': self.backend.EVICT_byte}
docs: Return dictionay with all stats at this level.