code: def __call__(self, key: str, values):
      assert key == self.key, f"Got {key}; expected {self.key}"
      self.aggregate(values)
  
file_path: ReAgent/reagent/core/tracker.py
imports: import functools
  import logging
  from typing import Dict, List, Type
  import torch
label_desc: Use image node_id 2 for calling the Aggregator obj's underlying member method code with example usage: obj.__call__(key, values) without return types