Clean and renumber a G-code program (Python)

"""Clean and renumber a G-code program: strip blank lines, renumber N-blocks,
and normalize decimal formatting on X/Y/Z/I/J/K/R words.

Usage:  python gcode_clean.py input.nc --out cleaned.nc
        python gcode_clean.py input.nc --start 10 --step 10
"""

import argparse
import re

WORD_RE = re.compile(r'([A-Z])(-?\d+\.?\d*)')


def clean_lines(lines, start=10, step=10, strip_comments=False):
    """Renumber N-blocks and normalize decimals. Returns the cleaned lines."""
    out = []
    n = start
    for raw in lines:
        line = raw.strip()
        if not line:
            continue
        if strip_comments and (line.startswith("(") or line.startswith(";")):
            continue

        # Drop any existing N-word so renumbering never collides with it
        line = re.sub(r'^N\d+\s*', '', line)

        def normalize(match):
            letter, value = match.groups()
            if letter in "XYZIJKR" and "." not in value:
                value += "."
            return f"{letter}{value}"

        line = WORD_RE.sub(normalize, line)

        if line.startswith("(") or line.startswith(";") or line.startswith("O"):
            out.append(line)  # comments/program numbers keep their own line, no N-word
        else:
            out.append(f"N{n} {line}")
            n += step
    return out


def main():
    ap = argparse.ArgumentParser(description=__doc__)
    ap.add_argument("file", help="G-code program to clean")
    ap.add_argument("--out", help="output file (default: print to stdout)")
    ap.add_argument("--start", type=int, default=10, help="first N-number")
    ap.add_argument("--step", type=int, default=10, help="N-number increment")
    ap.add_argument("--strip-comments", action="store_true",
                     help="drop comment-only lines instead of keeping them")
    args = ap.parse_args()

    with open(args.file) as fh:
        lines = fh.readlines()

    cleaned = clean_lines(lines, args.start, args.step, args.strip_comments)
    result = "\n".join(cleaned) + "\n"

    if args.out:
        with open(args.out, "w") as fh:
            fh.write(result)
        print(f"{len(cleaned)} lines written to {args.out}")
    else:
        print(result, end="")


if __name__ == "__main__":
    main()