"""
Minimal (byte-level) Byte Pair Encoding tokenizer.
Algorithmically follows along the GPT tokenizer:
https://github.com/openai/gpt-2/blob/master/src/encoder.py
Unlike BasicTokenizer:
- RegexTokenizer handles an optional regex splitting pattern.
- RegexTokenizer handles optional special tokens.
"""
import regex as re
from .base import Tokenizer, get_stats, merge
# the main GPT text split patterns, see
# https://github.com/openai/tiktoken/blob/main/tiktoken_ext/openai_public.py
GPT2_SPLIT_PATTERN = r"""'(?:[sdmt]|ll|ve|re)| ?\p{L}+| ?\p{N}+| ?[^\s\p{L}\p{N}]+|\s+(?!\S)|\s+"""
GPT4_SPLIT_PATTERN = r"""'(?i:[sdmt]|ll|ve|re)|[^\r\n\p{L}\p{N}]?+\p{L}+|\p{N}{1,3}| ?[^\s\p{L}\p{N}]++[\r\n]*|\s*[\r\n]|\s+(?!\S)|\s+"""
class RegexTokenizer(Tokenizer):
def __init__(self, pattern=None):
"""
- pattern: optional string to override the default (GPT-4 split pattern)
- special_tokens: str -> int dictionary of special tokens
example: {'<|endoftext|>': 100257}
"""
super().__init__()
self.pattern = GPT4_SPLIT_PATTERN if pattern is None else pattern
self.compiled_pattern = re.compile(self.pattern)
self.special_tokens = {}
self.inverse_special_tokens = {}
def train(self, text, vocab_size, verbose=False):
assert vocab_size >= 256
num_merges = vocab_size - 256
# split the text up into text chunks
text_chunks = re.findall(self.compiled_pattern, text)
# input text preprocessing
ids = [list(ch.encode("utf-8")) for ch in text_chunks]
# iteratively merge the most common pairs to create new tokens
merges = {} # (int, int) -> int
vocab = {idx: bytes([idx]) for idx in range(256)} # idx -> bytes
for i in range(num_merges):
# count the number of times every consecutive pair appears
stats = {}
for chunk_ids in ids:
# passing in stats will update it in place, adding up counts
get_stats(chunk_ids, stats)
# find the pair with the highest count
pair = max(stats, key=stats.get)
# mint a new token: assign it the next available id
idx = 256 + i
# replace all occurrences of pair in ids with idx
ids = [merge(chunk_ids, pair, idx) for chunk_ids in ids]
# save the merge
merges[pair] = idx
vocab[idx] = vocab[pair[0]] + vocab[pair[1]]
# prints
if verbose:
print(f"merge {i+1}/{num_merges}: {pair} -> {idx} ({vocab[idx]}) had {stats[pair]} occurrences")
# save class variables
self.merges = merges # used in encode()
self.vocab = vocab # used in decode()
def register_special_tokens(self, special_tokens):
# special_tokens is a dictionary of str -> int
# example: {"<|endoftext|>": 100257}
self.special_tokens = special_tokens
self.inverse_special_tokens = {v: k for k, v in special_tokens.items()}
def decode(self, ids):
# given ids (list of integers), return Python string
part_bytes = []
for idx in ids:
if idx in self.vocab:
part_bytes.append(self.vocab[idx])
elif idx in self.inverse_special_tokens:
part_bytes.append(self.inverse_special_tokens[idx].encode("utf-8"))
else:
raise ValueError(f"invalid token id: {idx}")
text_bytes = b"".join(part_bytes)
text = text_bytes.decode("utf-8", errors="replace")
return text
def _encode_chunk(self, text_bytes):
# return the token ids
# let's begin. first, convert all bytes to integers in range 0..255
ids = list(text_bytes)
while len(ids) >= 2:
# find the pair with the lowest merge index
stats = get_stats(ids)
pair = min(stats, key=lambda p: self.merges.get(p, float("inf")))
# subtle: if there are no more merges available, the key will
# result in an inf for every single pair, and the min will be
# just the first pair in the list, arbitrarily
# we can detect this terminating case by a membership check
if pair not in self.merges:
break # nothing else can be merged anymore
# otherwise let's merge the best pair (lowest merge index)
idx = self.merges[pair]
ids = merge(ids, pair, idx)
return ids
def encode_ordinary(self, text):
"""Encoding that ignores any special tokens."""
# split text into chunks of text by categories defined in regex pattern
text_chunks = re.findall(self.compiled_pattern, text)
# all chunks of text are encoded separately, then results are joined
ids = []
for chunk in text_chunks:
chunk_bytes = chunk.encode("utf-8") # raw bytes
chunk_ids = self._encode_chunk(chunk_bytes)
ids.extend(chunk_ids)
return ids
def encode(self, text, allowed_special="none_raise"):
"""
Unlike encode_ordinary, this function handles special tokens.
allowed_special: can be "all"|"none"|"none_raise" or a custom set of special tokens
if none_raise, then an error is raised if any special token is encountered in text
this is the default tiktoken behavior right now as well
any other behavior is either annoying, or a major footgun
"""
# decode the user desire w.r.t. handling of special tokens
special = None
if allowed_special == "all":
special = self.special_tokens
elif allowed_special == "none":
special = {}
elif allowed_special == "none_raise":
special = {}
assert all(token not in text for token in self.special_tokens)
elif isinstance(allowed_special, set):
special = {k: v for k, v in self.special_tokens.items() if k in allowed_special}
else:
raise ValueError(f"allowed_special={allowed_special} not understood")
if not special:
# shortcut: if no special tokens, just use the ordinary encoding
return self.encode_ordinary(text)
# otherwise, we have to be careful with potential special tokens in text
# we handle special tokens by splitting the text
# based on the occurrence of any exact match with any of the special tokens
# we can use re.split for this. note that surrounding the pattern with ()
# makes it into a capturing group, so the special tokens will be included
special_pattern = "(" + "|".join(re.escape(k) for k in special) + ")"
special_chunks = re.split(special_pattern, text)
# now all the special characters are separated from the rest of the text
# all chunks of text are encoded separately, then results are joined
ids = []
for part in special_chunks:
if part in special:
# this is a special token, encode it separately as a special case
ids.append(special[part])
else:
# this is an ordinary sequence, encode it normally
ids.extend(self.encode_ordinary(part))
return ids