src/extract_punct_template.py

"""Punctuation-template attention feature (Kostenok et al. 2024 §D).

For each sample we identify punctuation token positions via the tokenizer and
build a per-sample template mask T_mask[i, j] = 1 if token j is a punctuation
token, 0 otherwise. We then compute, per (layer, head):

    feature = 1 - sum(attn * T_mask) / sum(T_mask)

which is small when the head attends strongly to punctuation tokens and ~1
when the head ignores them.
"""
from __future__ import annotations

from pathlib import Path
from typing import List, Tuple

import numpy as np
import torch
from torch.utils.data import DataLoader
from tqdm import tqdm


PUNCT_CHARS = set(".,;:!?\"'`()[]{}-—–…")


def _punct_token_ids(tokenizer) -> set:
    """All token IDs whose decoded text is a punctuation-only string."""
    out = set()
    vocab = tokenizer.get_vocab()
    for tok, idx in vocab.items():
        # Decode the single token; strip BERT/RoBERTa's space/##/Ġ markers
        s = tok.replace("##", "").replace("Ġ", "").replace("▁", "")
        if s and all(c in PUNCT_CHARS for c in s):
            out.add(idx)
    return out


@torch.no_grad()
def compute_punct_template(attn_dir: Path, tokenizer, model_max_length: int,
                            df, text_col: str) -> Tuple[np.ndarray, List[str]]:
    L, H = 12, 12
    punct_ids = _punct_token_ids(tokenizer)
    rows = []
    for _, r in tqdm(df.reset_index(drop=True).iterrows(), total=len(df), desc="punct-template"):
        idx = int(r["idx"])
        # Re-tokenize to get per-token IDs for this sample
        enc = tokenizer(r[text_col], truncation=True, max_length=model_max_length,
                         padding="max_length", return_tensors="pt")
        ids = enc["input_ids"][0].tolist()
        is_punct = np.array([tid in punct_ids for tid in ids], dtype=np.float32)  # (T,)
        if is_punct.sum() == 0:
            # No punctuation tokens — feature defaults to 1.0
            rows.append(np.ones(L * H, dtype=np.float32))
            continue
        # Build template mask: every row attends to every punctuation position
        T = is_punct.shape[0]
        T_mask = np.tile(is_punct[None, :], (T, 1))                # (T, T)
        denom = float(T_mask.sum())
        # Load attention dump
        path = attn_dir / f"{idx:06d}.npz"
        with np.load(path, allow_pickle=True) as d:
            A = np.asarray(d["attn"]).astype(np.float32)            # (L, H, T_attn, T_attn)
        T_attn = A.shape[-1]
        T_mask = T_mask[:T_attn, :T_attn]
        denom = float(T_mask.sum())
        if denom <= 0:
            rows.append(np.ones(L * H, dtype=np.float32))
            continue
        feats = np.zeros(L * H, dtype=np.float32)
        for l in range(L):
            for h in range(H):
                feats[l * H + h] = 1.0 - float((A[l, h] * T_mask).sum() / denom)
        rows.append(feats)
    arr = np.stack(rows, axis=0).astype(np.float32)
    cols = [f"punct_L{l}H{h}" for l in range(L) for h in range(H)]
    return arr, cols