Python PyO3 Extensions: Port Hot Paths Without Full Rewrite Risk

# python/scoring.py — keep orchestration here
from typing import Sequence

try:
 from scorers_rs import score_batch as _score_batch_rs
 _IMPL = "rust"
except ImportError:
 _IMPL = "python"
 def _score_batch_rs(xs: Sequence[float], w: Sequence[float]) -> list[float]:
 return [sum(a * b for a, b in zip(row, w)) for row in xs] # fallback

def score_batch(rows: Sequence[Sequence[float]], weights: Sequence[float]) -> list[float]:
 # ✅ Single chokepoint — swap impl without call-site churn
 return list(_score_batch_rs(rows, weights))

// src/lib.rs — illustrative PyO3 surface
use pyo3::prelude::*;

#[pyfunction]
fn score_batch(rows: Vec<Vec<f64>>, weights: Vec<f64>) -> PyResult<Vec<f64>> {
 Ok(rows
 .into_iter()
 .map(|row| row.iter().zip(&weights).map(|(a, b)| a * b).sum())
 .collect())
}

#[pymodule]
fn scorers_rs(m: &Bound<'_>) -> PyResult<()> {
 m.add_function(wrap_pyfunction!(score_batch, m)?)?;
 Ok(())
}

# tests/test_score_parity.py
import json
from pathlib import Path
from scoring import score_batch

def test_parity_against_fixtures():
 for line in Path("testdata/score_cases.jsonl").read_text().splitlines():
 case = json.loads(line)
 out = score_batch(case["rows"], case["weights"])
 assert out == pytest.approx(case["expected"], rel=1e-9, abs=1e-9)

# Cargo.toml (excerpt)
[dependencies]
pyo3 = { version = "0.22", features = ["extension-module"] }