Rotate Log Files by Size in Python

import os
from pathlib import Path

def rotate_logs(directory: str, max_size: int = 100) -> None:
    """Rotate log files that exceed max_size bytes."""
    log_dir = Path(directory)
    for log_file in sorted(log_dir.glob("*.log"), key=lambda p: str(p)):
        if log_file.stat().st_size > max_size:
            for backup_num in range(10, 0, -1):
                backup = log_file.with_suffix(f".{backup_num}.log")
                next_backup = log_file.with_suffix(f".{backup_num + 1}.log")
                if backup.exists():
                    backup.rename(next_backup)
            log_file.rename(log_file.with_suffix(".1.log"))
            print(f"Rotated: {log_file}")

if __name__ == "__main__":
    # Create test log files
    test_dir = Path("test_logs")
    test_dir.mkdir(exist_ok=True)

    for name, size in [("app.log", 50), ("error.log", 150), ("debug.log", 250)]:
        path = test_dir / name
        path.write_bytes(b"x" * size)

    print("Initial log files:")
    for f in test_dir.glob("*.log"):
        print(f"  {f.name}: {f.stat().st_size} bytes")

    # Rotate files larger than 100 bytes
    rotate_logs(test_dir, max_size=100)

    print("\nAfter rotation:")
    for f in sorted(test_dir.glob("*.log")):
        print(f"  {f.name}: {f.stat().st_size} bytes")

    # Cleanup
    import shutil
    shutil.rmtree(test_dir)
    print("\nCleanup complete.")