Reassemble File Parts into Original File Bytes in Python

import os
import sys
from pathlib import Path

def reassemble_parts(parts_dir: Path, output_path: Path) -> int:
    """
    Reassemble file parts into the original file.

    Args:
        parts_dir: Directory containing the part files
        output_path: Path where the reassembled file will be written

    Returns:
        Number of bytes written
    """
    part_files = sorted(
        parts_dir.glob("part_*"),
        key=lambda p: int(p.stem.split("_")[1])
    )
    
    total_bytes = 0
    with open(output_path, "wb") as output:
        for part_file in part_files:
            with open(part_file, "rb") as part:
                data = part.read()
                output.write(data)
                total_bytes += len(data)
    
    return total_bytes

if __name__ == "__main__":
    parts_directory = Path("file_parts")
    output_file = Path("original_file.bin")
    
    bytes_written = reassemble_parts(parts_directory, output_file)
    print(f"Reassembled {len(list(parts_directory.glob('part_*')))} parts into {output_file} ({bytes_written} bytes)")