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"""
Base class for Tokenizers that can train a vocabulary from text, encode and decode strings into lists of integers and back.
The Tokenizer can also save and load its model to/from disk.
"""
from tokenizer.utils import render_token
class Tokenizer:
"""Base class for Tokenizers"""
def __init__(self):
# default: vocab size of 256 (all bytes), no merges, no patterns
self.merges = {} # (int, int) -> int
self.pattern = "" # str
self.special_tokens = {} # str -> int, e.g. {'<|endoftext|>': 100257}
self.vocab = self._build_vocab() # int -> bytes
def train(self, text, vocab_size, verbose=False):
# Tokenizer can train a vocabulary of size vocab_size from text
raise NotImplementedError
def encode(self, text):
# Tokenizer can encode a string into a list of integers
raise NotImplementedError
def decode(self, ids):
# Tokenizer can decode a list of integers into a string
raise NotImplementedError
def _build_vocab(self):
# vocab is simply and deterministically derived from merges
vocab = {idx: bytes([idx]) for idx in range(256)}
for (p0, p1), idx in self.merges.items():
vocab[idx] = vocab[p0] + vocab[p1]
for special, idx in self.special_tokens.items():
vocab[idx] = special.encode("utf-8")
return vocab
def save(self, file_prefix):
"""
Saves two files: file_prefix.vocab and file_prefix.model
This is inspired (but not equivalent to!) sentencepiece's model saving:
- model file is the critical one, intended for load()
- vocab file is just a pretty printed version for human inspection only
"""
# write the model: to be used in load() later
model_file = file_prefix + ".model"
with open(model_file, "w") as f:
# write the version, pattern and merges, that's all that's needed
f.write("minbpe v1\n")
f.write(f"{self.pattern}\n")
# write the special tokens, first the number of them, then each one
f.write(f"{len(self.special_tokens)}\n")
for special, idx in self.special_tokens.items():
f.write(f"{special} {idx}\n")
# the merges dict
for idx1, idx2 in self.merges:
f.write(f"{idx1} {idx2}\n")
# write the vocab: for the human to look at
vocab_file = file_prefix + ".vocab"
inverted_merges = {idx: pair for pair, idx in self.merges.items()}
with open(vocab_file, "w", encoding="utf-8") as f:
for idx, token in self.vocab.items():
# note: many tokens may be partial utf-8 sequences
# and cannot be decoded into valid strings. Here we're using
# errors='replace' to replace them with the replacement char �.
# this also means that we couldn't possibly use .vocab in load()
# because decoding in this way is a lossy operation!
s = render_token(token)
# find the children of this token, if any
if idx in inverted_merges:
# if this token has children, render it nicely as a merge
idx0, idx1 = inverted_merges[idx]
s0 = render_token(self.vocab[idx0])
s1 = render_token(self.vocab[idx1])
f.write(f"[{s0}][{s1}] -> [{s}] {idx}\n")
else:
# otherwise this is leaf token, just print it
# (this should just be the first 256 tokens, the bytes)
f.write(f"[{s}] {idx}\n")
def load(self, model_file):
"""Inverse of save() but only for the model file"""
assert model_file.endswith(".model")
# read the model file
merges = {}
special_tokens = {}
idx = 256
with open(model_file, "r", encoding="utf-8") as f:
# read the version
version = f.readline().strip()
assert version == "minbpe v1"
# read the pattern
self.pattern = f.readline().strip()
# read the special tokens
num_special = int(f.readline().strip())
for _ in range(num_special):
special, special_idx = f.readline().strip().split()
special_tokens[special] = int(special_idx)
# read the merges
for line in f:
idx1, idx2 = map(int, line.split())
merges[(idx1, idx2)] = idx
idx += 1
self.merges = merges
self.special_tokens = special_tokens
self.vocab = self._build_vocab()
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