docstr: Lower text and remove punctuation, articles and extra whitespace.
docstr_tok: ["Lower","text","and","remove","punctuation",",","articles","and","extra","whitespace","."]
code: def _normalize_answer(self, s: str):
      """Lower text and remove punctuation, articles and extra whitespace."""
  
      def white_space_fix(text):
          return " ".join(text.split())
  
      def remove_articles(text):
          regex = re.compile(r"\b(a|an|the)\b", re.UNICODE)
          return re.sub(regex, " ", text)
  
      def remove_punc(text):
          exclude = set(string.punctuation)
          return "".join(ch for ch in text if ch not in exclude)
  
      def lower(text):
          return text.lower()
  
      return white_space_fix(remove_articles(remove_punc(lower(s))))
  
imports: import re
  import string
  from typing import Dict, List, Set, Tuple, Union
  import numpy
  from pytext.common.constants import Stage
  from pytext.metric_reporters.channel import Channel, ConsoleChannel, FileChannel
  from pytext.metric_reporters.metric_reporter import MetricReporter
  from pytext.metrics.squad_metrics import SquadMetrics
  from pytext.utils.data import merge_token_labels_to_slot, parse_slot_string, Slot
  from scipy.optimize import linear_sum_assignment
label_desc: Use image node_id 15 for calling the MultiSpanQAMetricReporter obj's underlying member method code with example usage: obj._normalize_answer(s) and returns: white_space_fix, str, re, str, text