old_contents: """
  A :class:`~allennlp.training.metrics.metric.Metric` is some quantity or quantities
  that can be accumulated during training or evaluation; for example,
  accuracy or F1 score.
  """
  
  from allennlp.training.metrics.attachment_scores import AttachmentScores
  from allennlp.training.metrics.average import Average
  from allennlp.training.metrics.boolean_accuracy import BooleanAccuracy
  from allennlp.training.metrics.bleu import BLEU
  from allennlp.training.metrics.categorical_accuracy import CategoricalAccuracy
  from allennlp.training.metrics.conll_coref_scores import ConllCorefScores
  from allennlp.training.metrics.covariance import Covariance
  from allennlp.training.metrics.entropy import Entropy
  from allennlp.training.metrics.evalb_bracketing_scorer import EvalbBracketingScorer, DEFAULT_EVALB_DIR
  from allennlp.training.metrics.fbeta_measure import FBetaMeasure
  from allennlp.training.metrics.f1_measure import F1Measure
  from allennlp.training.metrics.mean_absolute_error import MeanAbsoluteError
  from allennlp.training.metrics.mention_recall import MentionRecall
  from allennlp.training.metrics.metric import Metric
  from allennlp.training.metrics.pearson_correlation import PearsonCorrelation
  from allennlp.training.metrics.perplexity import Perplexity
  from allennlp.training.metrics.sequence_accuracy import SequenceAccuracy
  from allennlp.training.metrics.span_based_f1_measure import SpanBasedF1Measure
  from allennlp.training.metrics.squad_em_and_f1 import SquadEmAndF1
  from allennlp.training.metrics.srl_eval_scorer import SrlEvalScorer, DEFAULT_SRL_EVAL_PATH
  from allennlp.training.metrics.unigram_recall import UnigramRecall
  from allennlp.training.metrics.auc import Auc
  
new_contents: """
  A :class:`~allennlp.training.metrics.metric.Metric` is some quantity or quantities
  that can be accumulated during training or evaluation; for example,
  accuracy or F1 score.
  """
  
  from allennlp.training.metrics.attachment_scores import AttachmentScores
  from allennlp.training.metrics.average import Average
  from allennlp.training.metrics.boolean_accuracy import BooleanAccuracy
  from allennlp.training.metrics.bleu import BLEU
  from allennlp.training.metrics.categorical_accuracy import CategoricalAccuracy
  from allennlp.training.metrics.conll_coref_scores import ConllCorefScores
  from allennlp.training.metrics.covariance import Covariance
  from allennlp.training.metrics.drop_em_and_f1 import DropEmAndF1
  from allennlp.training.metrics.entropy import Entropy
  from allennlp.training.metrics.evalb_bracketing_scorer import EvalbBracketingScorer, DEFAULT_EVALB_DIR
  from allennlp.training.metrics.fbeta_measure import FBetaMeasure
  from allennlp.training.metrics.f1_measure import F1Measure
  from allennlp.training.metrics.mean_absolute_error import MeanAbsoluteError
  from allennlp.training.metrics.mention_recall import MentionRecall
  from allennlp.training.metrics.metric import Metric
  from allennlp.training.metrics.pearson_correlation import PearsonCorrelation
  from allennlp.training.metrics.perplexity import Perplexity
  from allennlp.training.metrics.sequence_accuracy import SequenceAccuracy
  from allennlp.training.metrics.span_based_f1_measure import SpanBasedF1Measure
  from allennlp.training.metrics.squad_em_and_f1 import SquadEmAndF1
  from allennlp.training.metrics.srl_eval_scorer import SrlEvalScorer, DEFAULT_SRL_EVAL_PATH
  from allennlp.training.metrics.unigram_recall import UnigramRecall
  from allennlp.training.metrics.auc import Auc
  
subject: Add DropEmAndF1 metric to __init__.py (#3191)