text: import os
  import re
  from lm_eval.base import rf, PerplexityTask
  from lm_eval.utils import sh
  
  from best_download import download_file
  
  
  def wikitext_detokenizer(string):
      # contractions
      string = string.replace("s '", "s'")
      string = re.sub(r"/' [0-9]/", r"/'[0-9]/", string)
      # number separators
      string = string.replace(" @-@ ", "-")
      string = string.replace(" @,@ ", ",")
      string = string.replace(" @.@ ", ".")
      # punctuation
      string = string.replace(" : ", ": ")
      string = string.replace(" ; ", "; ")
      string = string.replace(" . ", ". ")
      string = string.replace(" ! ", "! ")
      string = string.replace(" ? ", "? ")
      string = string.replace(" , ", ", ")
      # double brackets
      string = re.sub(r"\(\s*([^\)]*?)\s*\)", r"(\1)", string)
      string = re.sub(r"\[\s*([^\]]*?)\s*\]", r"[\1]", string)
      string = re.sub(r"{\s*([^}]*?)\s*}", r"{\1}", string)
      string = re.sub(r"\"\s*([^\"]*?)\s*\"", r'"\1"', string)
      string = re.sub(r"'\s*([^']*?)\s*'", r"'\1'", string)
      # miscellaneous
      string = string.replace("= = = =", "====")
      string = string.replace("= = =", "===")
      string = string.replace("= =", "==")
      string = string.replace(" " + chr(176) + " ", chr(176))
      string = string.replace(" \n", "\n")
      string = string.replace("\n ", "\n")
      string = string.replace(" N ", " 1 ")
      string = string.replace(" 's", "'s")
  
      return string
  
  
  class WikiText(PerplexityTask):
      VERSION = 1
  
      def download(self):
          if not os.path.exists('data/wikitext/wikitext-2-raw/wiki.valid.raw'):
              os.makedirs("data/wikitext/", exist_ok=True)
              download_file("https://s3.amazonaws.com/research.metamind.io/wikitext/wikitext-2-raw-v1.zip", local_file="data/wikitext/wikitext-2-raw-v1.zip", expected_checksum="ef7edb566e3e2b2d31b29c1fdb0c89a4cc683597484c3dc2517919c615435a11")
              sh("cd data/wikitext/ && unzip wikitext-2-raw-v1.zip")
  
      def has_validation_docs(self):
          return True
  
      def has_train_docs(self):
          return True
  
      def has_test_docs(self):
          return True
      
      def docs_for_split(self, split):
          ret = []
          for line in open(f"data/wikitext/wikitext-2-raw/wiki.{split}.raw").read().split('\n'):
              rline = line.replace("= = =", "===").replace("= =", "==").strip()
              if rline.startswith('= ') and rline.strip().endswith(' ='):
                  s = '\n'.join(ret)
                  if s.strip(): yield s
                  ret = []
              ret.append(line)
          yield '\n'.join(ret)
  
      def validation_docs(self):
          return self.docs_for_split('valid')
  
      def train_docs(self):
          return self.docs_for_split('train')
  
      def test_docs(self):
          return self.docs_for_split('test')
  
      def doc_to_target(self, doc):
          return wikitext_detokenizer(doc)
      
      def count_words(self, doc):
          # count number of words in *original doc before detokenization*
          return len(re.split(r"\s+", doc))
  