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"""Training loop. Usage: python -m src.train [model] [seed] [--flag ...]"""
import csv
import math
import os
import random
import numpy as np
import torch
import torch.nn as nn
from src.config import Config, parse_args
from src.data import build_examples, decode_tokens, get_splits, make_batch
from src.model_api import build_model, greedy_decode
def set_seed(s: int) -> None:
random.seed(s)
np.random.seed(s)
torch.manual_seed(s)
@torch.no_grad()
def evaluate(model, examples, cfg: Config):
"""Token accuracy (teacher-forced) + exact-match accuracy (greedy) + per-example detail."""
model.eval()
token_correct = 0
token_total = 0
em_correct = 0
per_example = []
for x, target in examples:
batch = make_batch([(x, target)], cfg)
out = model(batch["x"], batch["y_in"])
logits = out["logits"][0]
y = batch["y"][0]
mask = batch["y_mask"][0]
pred_tok = logits.argmax(-1)
token_correct += int((pred_tok[mask] == y[mask]).sum())
token_total += int(mask.sum())
xi = torch.tensor(x, dtype=torch.long).unsqueeze(0)
gen = greedy_decode(model, xi, cfg)[0].tolist()
pred = decode_tokens(gen, cfg)
target_n = decode_tokens(target, cfg)
ok = pred == target_n
em_correct += int(ok)
per_example.append((tuple(x), target_n, pred, ok))
model.train()
return token_correct / max(1, token_total), em_correct / len(examples), per_example
def log_example_rows(log_examples, val_per_example):
"""Format the fixed 10 logged val inputs as '42:ok' strings, in fixed order."""
by_x = {x: (target, pred, ok) for x, target, pred, ok in val_per_example}
rows = []
for x, _target in log_examples:
t, p, ok = by_x[tuple(x)]
label = "".join(map(str, x)) # "42" in both vocab modes
rows.append(f"{label}:{'ok' if ok else f'{p}~{t}'}")
return ";".join(rows)
def main() -> None:
cfg = parse_args()
set_seed(cfg.seed)
out_dir = os.path.join(cfg.out_dir, cfg.model, f"seed{cfg.seed}")
os.makedirs(out_dir, exist_ok=True)
cfg.save(os.path.join(out_dir, "config.json"))
train_in, val_in = get_splits(cfg)
train_ex = build_examples(train_in, cfg)
val_ex = build_examples(val_in, cfg)
model = build_model(cfg)
print(f"model={cfg.model} params={model.param_count()} train={len(train_ex)} val={len(val_ex)} "
f"vocab={cfg.vocab} eos={cfg.eos_id} pad={cfg.pad_id}")
opt = torch.optim.AdamW(model.parameters(), lr=cfg.lr, weight_decay=cfg.weight_decay)
ce = nn.CrossEntropyLoss(reduction="none")
log_examples = sorted(val_ex, key=lambda x: (len(str(x)), x))[: cfg.log_n_examples]
csv_path = os.path.join(out_dir, "metrics.csv")
fieldnames = ["step", "train_loss", "train_token_acc", "train_em", "val_token_acc",
"val_em", "mean_halt_steps", "log_examples", "param_count"]
best_val_em = -1.0
patience_left = cfg.early_stop_patience
best_path = os.path.join(out_dir, "best.pt")
n_batches = math.ceil(len(train_ex) / cfg.batch_size)
rng = random.Random(cfg.seed)
step = 0
done = False
first_row = True
def _eval_pass(cur_loss, halt_steps):
nonlocal best_val_em, patience_left, done, first_row
train_tok, train_em, _ = evaluate(model, train_ex, cfg)
val_tok, val_em, val_per = evaluate(model, val_ex, cfg)
mean_halt = float(halt_steps.mean()) if halt_steps is not None else float("nan")
row = {
"step": step, "train_loss": float(cur_loss), "train_token_acc": train_tok,
"train_em": train_em, "val_token_acc": val_tok, "val_em": val_em,
"mean_halt_steps": mean_halt,
"log_examples": log_example_rows(log_examples, val_per),
"param_count": model.param_count(),
}
with open(csv_path, "a", newline="") as fh:
w = csv.DictWriter(fh, fieldnames=fieldnames)
if first_row:
w.writeheader()
first_row = False
w.writerow(row)
if val_em > best_val_em:
best_val_em = val_em
torch.save(model.state_dict(), best_path)
if val_em >= cfg.early_stop_em:
patience_left -= 1
else:
patience_left = cfg.early_stop_patience
if patience_left <= 0:
done = True
print(f"step {step} loss {float(cur_loss):.4f} train_em {train_em:.3f} "
f"val_em {val_em:.3f} val_tok {val_tok:.3f} halt {mean_halt:.2f}")
while step < cfg.max_train_steps and not done:
rng.shuffle(train_ex)
for bi in range(n_batches):
sl = train_ex[bi * cfg.batch_size: (bi + 1) * cfg.batch_size]
if not sl:
continue
batch = make_batch(sl, cfg)
out = model(batch["x"], batch["y_in"])
logits = out["logits"]
y_safe = batch["y"].clamp(max=cfg.vocab - 1) # CE index guard for pad positions
loss_tokens = ce(logits.reshape(-1, cfg.vocab), y_safe.reshape(-1)).reshape(
logits.shape[0], -1) * batch["y_mask"].float()
loss_tokens = loss_tokens.sum() / batch["y_mask"].sum().clamp(min=1)
if cfg.halting and step >= cfg.halt_warmup_steps:
if step >= cfg.halt_ramp_end_steps:
lam = cfg.halt_penalty
else:
frac = (step - cfg.halt_warmup_steps) / max(1, cfg.halt_ramp_end_steps - cfg.halt_warmup_steps)
lam = cfg.halt_penalty * frac
else:
lam = 0.0
halt = out["halt_steps"]
penalty = halt.float().mean() * lam if halt is not None and lam > 0 else 0.0
loss = loss_tokens + penalty
opt.zero_grad()
loss.backward()
opt.step()
step += 1
if step % cfg.eval_every == 0 or step >= cfg.max_train_steps:
_eval_pass(loss.detach(), halt.detach() if halt is not None else None)
if done:
break
torch.save(model.state_dict(), os.path.join(out_dir, "last.pt"))
print(f"DONE steps={step} best_val_em={best_val_em:.4f}")
if __name__ == "__main__":
main()
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