1  """Byte pair encoding utilities"""
   2  
   3  import os
   4  import json
   5  import regex as re
   6  from functools import lru_cache
   7  
   8  @lru_cache()
   9  def bytes_to_unicode():
  10      """
  11      Returns list of utf-8 byte and a corresponding list of unicode strings.
  12      The reversible bpe codes work on unicode strings.
  13      This means you need a large # of unicode characters in your vocab if you want to avoid UNKs.
  14      When you're at something like a 10B token dataset you end up needing around 5K for decent coverage.
  15      This is a signficant percentage of your normal, say, 32K bpe vocab.
  16      To avoid that, we want lookup tables between utf-8 bytes and unicode strings.
  17      And avoids mapping to whitespace/control characters the bpe code barfs on.
  18      """
  19      bs = list(range(ord("!"), ord("~")+1))+list(range(ord("¡"), ord("¬")+1))+list(range(ord("®"), ord("ÿ")+1))
  20      cs = bs[:]
  21      n = 0
  22      for b in range(2**8):
  23          if b not in bs:
  24              bs.append(b)
  25              cs.append(2**8+n)
  26              n += 1
  27      cs = [chr(n) for n in cs]
  28      return dict(zip(bs, cs))
  29  
  30  def get_pairs(word):
  31      """Return set of symbol pairs in a word.
  32  
  33      Word is represented as tuple of symbols (symbols being variable-length strings).
  34      """
  35      pairs = set()
  36      prev_char = word[0]
  37      for char in word[1:]:
  38          pairs.add((prev_char, char))
  39          prev_char = char
  40      return pairs
  41  
  42  class Encoder:
  43      def __init__(self, encoder, bpe_merges, errors='replace'):
  44          self.encoder = encoder
  45          self.decoder = {v:k for k,v in self.encoder.items()}
  46          self.errors = errors # how to handle errors in decoding
  47          self.byte_encoder = bytes_to_unicode()
  48          self.byte_decoder = {v:k for k, v in self.byte_encoder.items()}
  49          self.bpe_ranks = dict(zip(bpe_merges, range(len(bpe_merges))))
  50          self.cache = {}
  51  
  52          # Should haved added re.IGNORECASE so BPE merges can happen for capitalized versions of contractions
  53          self.pat = re.compile(r"""'s|'t|'re|'ve|'m|'ll|'d| ?\p{L}+| ?\p{N}+| ?[^\s\p{L}\p{N}]+|\s+(?!\S)|\s+""")
  54  
  55      def bpe(self, token):
  56          if token in self.cache:
  57              return self.cache[token]
  58          word = tuple(token)
  59          pairs = get_pairs(word)
  60  
  61          if not pairs:
  62              return token
  63  
  64          while True:
  65              bigram = min(pairs, key = lambda pair: self.bpe_ranks.get(pair, float('inf')))
  66              if bigram not in self.bpe_ranks:
  67                  break
  68              first, second = bigram
  69              new_word = []
  70              i = 0
  71              while i < len(word):
  72                  try:
  73                      j = word.index(first, i)
  74                      new_word.extend(word[i:j])
  75                      i = j
  76                  except:
  77                      new_word.extend(word[i:])
  78                      break
  79  
  80                  if word[i] == first and i < len(word)-1 and word[i+1] == second:
  81                      new_word.append(first+second)
  82                      i += 2
  83                  else:
  84                      new_word.append(word[i])
  85                      i += 1
  86              new_word = tuple(new_word)
  87              word = new_word
  88              if len(word) == 1:
  89                  break
  90              else:
  91                  pairs = get_pairs(word)
  92          word = ' '.join(word)
  93          self.cache[token] = word
  94          return word
  95  
  96      def encode(self, text):
  97          bpe_tokens = []
  98          for token in re.findall(self.pat, text):
  99              token = ''.join(self.byte_encoder[b] for b in token.encode('utf-8'))
 100              bpe_tokens.extend(self.encoder[bpe_token] for bpe_token in self.bpe(token).split(' '))
 101          return bpe_tokens
 102  
 103      def decode(self, tokens):
 104          text = ''.join([self.decoder[token] for token in tokens])
 105          text = bytearray([self.byte_decoder[c] for c in text]).decode('utf-8', errors=self.errors)
 106          return text
 107  
 108  def get_encoder(model_name, models_dir):
 109      with open(os.path.join(models_dir, model_name, 'encoder.json'), 'r') as f:
 110          encoder = json.load(f)
 111      with open(os.path.join(models_dir, model_name, 'vocab.bpe'), 'r', encoding="utf-8") as f:
 112          bpe_data = f.read()
 113      bpe_merges = [tuple(merge_str.split()) for merge_str in bpe_data.split('\n')[1:-1]]
 114      return Encoder(
 115          encoder=encoder,
 116          bpe_merges=bpe_merges,
 117      )
 118