text: """
  Byte pair encoding utilities from GPT-2.
  
  Original source: https://github.com/openai/gpt-2/blob/master/src/encoder.py
  Original license: MIT
  """
  
  import json
  from functools import lru_cache
  
  
  @lru_cache()
  def bytes_to_unicode():
      """
      Returns list of utf-8 byte and a corresponding list of unicode strings.
      The reversible bpe codes work on unicode strings.
      This means you need a large # of unicode characters in your vocab if you want to avoid UNKs.
      When you're at something like a 10B token dataset you end up needing around 5K for decent coverage.
      This is a signficant percentage of your normal, say, 32K bpe vocab.
      To avoid that, we want lookup tables between utf-8 bytes and unicode strings.
      And avoids mapping to whitespace/control characters the bpe code barfs on.
      """
      bs = (
          list(range(ord("!"), ord("~") + 1))
          + list(range(ord("¡"), ord("¬") + 1))
          + list(range(ord("®"), ord("ÿ") + 1))
      )
      cs = bs[:]
      n = 0
      for b in range(2**8):
          if b not in bs:
              bs.append(b)
              cs.append(2**8 + n)
              n += 1
      cs = [chr(n) for n in cs]
      return dict(zip(bs, cs))
  
  
  def get_pairs(word):
      """Return set of symbol pairs in a word.
      Word is represented as tuple of symbols (symbols being variable-length strings).
      """
      pairs = set()
      prev_char = word[0]
      for char in word[1:]:
          pairs.add((prev_char, char))
          prev_char = char
      return pairs
  
  
  class Encoder:
      def __init__(self, encoder, bpe_merges, errors="replace"):
          self.encoder = encoder
          self.decoder = {v: k for k, v in self.encoder.items()}
          self.errors = errors  # how to handle errors in decoding
          self.byte_encoder = bytes_to_unicode()
          self.byte_decoder = {v: k for k, v in self.byte_encoder.items()}
          self.bpe_ranks = dict(zip(bpe_merges, range(len(bpe_merges))))
          self.cache = {}
  
          try:
              import regex as re
  
              self.re = re
          except ImportError:
              raise ImportError("Please install regex with: pip install regex")
  
          # Should haved added re.IGNORECASE so BPE merges can happen for capitalized versions of contractions
          self.pat = self.re.compile(
              r"""'s|'t|'re|'ve|'m|'ll|'d| ?\p{L}+| ?\p{N}+| ?[^\s\p{L}\p{N}]+|\s+(?!\S)|\s+"""
          )
  
      def bpe(self, token):
          if token in self.cache:
              return self.cache[token]
          word = tuple(token)
          pairs = get_pairs(word)
  
          if not pairs:
              return token
  
          while True:
              bigram = min(pairs, key=lambda pair: self.bpe_ranks.get(pair, float("inf")))
              if bigram not in self.bpe_ranks:
                  break
              first, second = bigram
              new_word = []
              i = 0
              while i < len(word):
                  try:
                      j = word.index(first, i)
                      new_word.extend(word[i:j])
                      i = j
                  except:
                      new_word.extend(word[i:])
                      break
  
                  if word[i] == first and i < len(word) - 1 and word[i + 1] == second:
                      new_word.append(first + second)
                      i += 2
                  else:
                      new_word.append(word[i])
                      i += 1
              new_word = tuple(new_word)
              word = new_word
              if len(word) == 1:
                  break
              else:
                  pairs = get_pairs(word)
          word = " ".join(word)
          self.cache[token] = word
          return word
  
      def encode(self, text):
          bpe_tokens = []
          for token in self.re.findall(self.pat, text):
              token = "".join(self.byte_encoder[b] for b in token.encode("utf-8"))
              bpe_tokens.extend(
                  self.encoder[bpe_token] for bpe_token in self.bpe(token).split(" ")
              )
          return bpe_tokens
  
      def decode(self, tokens):
          text = "".join([self.decoder.get(token, token) for token in tokens])
          text = bytearray([self.byte_decoder[c] for c in text]).decode(
              "utf-8", errors=self.errors
          )
          return text
  
  
  def get_encoder(encoder_json_path, vocab_bpe_path):
      with open(encoder_json_path, "r") as f:
          encoder = json.load(f)
      with open(vocab_bpe_path, "r", encoding="utf-8") as f:
          bpe_data = f.read()
      bpe_merges = [tuple(merge_str.split()) for merge_str in bpe_data.split("\n")[1:-1]]
      return Encoder(
          encoder=encoder,
          bpe_merges=bpe_merges,
      )
  