from pathlib import Path


def list_files(path='.', extension=''):
    """Return list of files with specific extension in path.

    - by default, return all files with any extension.
    - directories are excluded
    - results are sorted by name
    """
    folder = Path(path)
    pattern = '*' + extension
    paths = folder.glob(pattern)
    files = [p for p in paths if p.is_file()]
    return sorted(files)