char128_shift_tokenizer

char128-shift Tokenizer

A fixed-size Hugging Face–compatible character tokenizer with a dedicated SHIFT token (↨) to represent uppercase letters. Instead of assigning separate tokens to uppercase A–Z, each uppercase is encoded as ↨ + lowercase (e.g., H → ↨h).

This repository contains the ready-to-use tokenizer, which can be loaded with AutoTokenizer, as well as the script that made it (in src\ folder)

---

Features

• Fixed 128-token vocabulary (including specials).
• Uppercase encoding via SHIFT token, no duplicate uppercase letters in vocab.
• WordLevel model with explicit closed character set.
• Pre-tokenizer splits by Unicode grapheme clusters (\X), so emoji and diacritics are preserved.
• Normalizer maps A–Z → ↨ + lowercase explicitly.
• Decoder concatenates tokens directly (no extra spaces).

---

Installation

You only need transformers (for Python interface) and optionally tokenizers (for advanced building).

pip install transformers>=4.40 tokenizers>=0.14

No PyTorch/TensorFlow/Flax required to use the tokenizer itself.

---

Usage

from transformers import AutoTokenizer

# Replace with your Hub repo
tok = AutoTokenizer.from_pretrained("Corianas/char128_shift_tokenizer")

print(tok.vocab_size)  # 128
ids = tok.encode("Hello, There!\n<eos>")
print(ids)
print(tok.decode(ids, skip_special_tokens=True, clean_up_tokenization_spaces=False))
# → "↨hello, ↨there!\n<eos>"

---

Restoring Uppercase

The decode output will show SHIFT markers (e.g., ↨h). For display, restore casing:

def restore_uppercase(s: str, shift="↨"):
    out, i, n = [], 0, len(s)
    while i < n:
        if s[i] == shift and i+1 < n and s[i+1] != shift:
            out.append(s[i+1].upper()); i += 2
        else:
            out.append(s[i]); i += 1
    return "".join(out)

ids = tok.encode("Hello, There!\n<eos>")
decoded = tok.decode(ids, skip_special_tokens=True, clean_up_tokenization_spaces=False)
print(decoded)                  # "↨hello, ↨there!\n<eos>"
print(restore_uppercase(decoded))  # "Hello, There!\n<eos>"

---

Vocabulary

The 128 tokens include:

• Lowercase letters a–z
• Digits 0–9
• Whitespace (space, \n, \t)
• Punctuation and symbols (configurable)
• Diacritics like è, é if needed
• Special tokens <pad>, <unk>, <bos>, <eos>
• SHIFT token ↨

Uppercase A–Z are not in vocab — they are represented via SHIFT.

---

Integration

For dataset preparation:

import numpy as np, os
from transformers import AutoTokenizer

tok = AutoTokenizer.from_pretrained("char128_shift_tokenizer")

with open("input.txt", "r", encoding="utf-8") as f:
    data = f.read()
n = len(data)
train_txt, val_txt = data[:int(0.9*n)], data[int(0.9*n):]

train_ids = tok.encode(train_txt)
val_ids   = tok.encode(val_txt)

np.array(train_ids, dtype=np.uint16).tofile("train.bin")
np.array(val_ids, dtype=np.uint16).tofile("val.bin")

Your model’s vocab_size must match (128).

---

Known Edge Cases

• Non-ASCII uppercase (like À, É) are lowercased without SHIFT unless you add explicit rules.
• Spaces in decode are disabled by setting decoder to concat; if you see them, ensure your tokenizer was saved with tok.decoder = decoders.Sequence([]).
• Unknown chars → <unk>. Ensure your vocab includes everything you expect.

---

License

MIT

---

Example Test

from transformers import AutoTokenizer

tok = AutoTokenizer.from_pretrained("Corianas/char128_shift_tokenizer")
ids = tok.encode("Hello, There!\n<eos>")
print(ids)
print(tok.decode(ids, skip_special_tokens=True, clean_up_tokenization_spaces=False))
# ↨hello, ↨there!\n<eos>