src/export_parquet.py

#!/usr/bin/env python
"""Export the SCP dataset to Parquet -- one file per table.

Writes `<out>/pages.parquet`, `<out>/page_tags.parquet` and
`<out>/page_alternate_titles.parquet` (zstd-compressed), ready for publishing.
Re-running overwrites the files.

Usage (run from the src/ directory, like scp_dataset.py):
    python export_parquet.py
    python export_parquet.py --db ../data/scp_dataset.duckdb --out ../data/parquet
"""

from __future__ import annotations

import argparse
import logging
from pathlib import Path

import duckdb

DEFAULT_DB = "../data/scp_dataset.duckdb"
DEFAULT_OUT = "../data/parquet"
DEFAULT_COMPRESSION = "zstd"

_TABLES: tuple[str, ...] = ("pages", "page_tags", "page_alternate_titles")

logger = logging.getLogger("export_parquet")


def export_table(
    con: duckdb.DuckDBPyConnection,
    out_dir: Path,
    table: str,
    compression: str,
) -> None:
    """Write one table to `out_dir/<table>.parquet` and log its row count."""
    target = out_dir / f"{table}.parquet"

    # `table` is an internal constant; COPY returns the number of rows written.
    result = con.execute(
        f"COPY {table} TO '{target}' (FORMAT PARQUET, COMPRESSION '{compression}')"
    ).fetchone()

    rows = int(result[0]) if result else 0
    logger.info("%-22s %s rows -> %s", table, f"{rows:,}", target)


def main(argv: list[str] | None = None) -> int:
    """Parse arguments and export every table to a Parquet file."""
    parser = argparse.ArgumentParser(
        description="Export the SCP dataset to Parquet (one file per table).",
        formatter_class=argparse.ArgumentDefaultsHelpFormatter,
    )

    parser.add_argument("--db", default=DEFAULT_DB, help="DuckDB database path")
    parser.add_argument("--out", default=DEFAULT_OUT, help="Output directory")
    parser.add_argument(
        "--compression",
        default=DEFAULT_COMPRESSION,
        help="Parquet codec",
    )

    args = parser.parse_args(argv)

    logging.basicConfig(
        level=logging.INFO,
        format="%(asctime)s %(levelname)-7s %(message)s",
        datefmt="%H:%M:%S",
    )
    out_dir = Path(args.out)
    out_dir.mkdir(parents=True, exist_ok=True)  # DuckDB won't create missing parents.

    con = duckdb.connect(args.db, read_only=True)
    try:
        for table in _TABLES:
            export_table(con, out_dir, table, args.compression)
    finally:
        con.close()

    logger.info("Done. Parquet written under %s/", out_dir)
    return 0


if __name__ == "__main__":
    raise SystemExit(main())