class_docstr: Normalized discounted cumulative gain metric.
docstr: :return: Formated string representation of the metric.
docstr_tok: [":","return",":","Formated","string","representation","of","the","metric","."]
code: def __repr__(self) -> str:
      """:return: Formated string representation of the metric."""
      return f"{self.ALIAS[0]}@{self._k}({self._threshold})"
  
imports: import numpy
  from matchzoo.engine.base_metric import BaseMetric, sort_and_couple
  from .discounted_cumulative_gain import DiscountedCumulativeGain
label_desc: Use image node_id 2 for calling the NormalizedDiscountedCumulativeGain obj's underlying member method code with example usage: obj.__repr__() and returns: self, str, self, str, self, str