class_docstr: :class:`AbstractEvaluator` is an abstract object which supports
  the evaluation of the model. It is called by :class:`Trainer`.
  
  Note:       
      If you want to inherit this class and implement your own evalautor class, 
      you must implement the following functions.
  
  Args:
      config (Config): The config of evaluator.
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docstr: to calculate the metrics
docstr_tok: ["to","calculate","the","metrics"]
code: def _calc_metrics_info(self):
      """to calculate the metrics"""
      raise NotImplementedError
  
imports: import numpy
label_desc: Use image node_id 3 for calling the AbstractEvaluator obj's underlying member method code with example usage: obj._calc_metrics_info() without return types