class_docstr: Call the callback function with epoch # when the epoch ends
class_docstr_tok: ["Call","the","callback","function","with","epoch","#","when","the","epoch","ends"]
code: def update(self, key: str, value):
      self.callback(value)
  
imports: import logging
  from typing import Any, Dict, Iterable, List, Optional
  from reagent.core.tensorboardX import SummaryWriterContext
  from reagent.core.tracker import Aggregator, Observer
label_desc: Use image node_id 2 for calling the EpochEndObserver obj's underlying member method code with example usage: obj.update(key, value) without return types