import random
import string


def _random_filename(filename, k=8):
    """Random Filename

    :param filename: The original filename. Can be a path
    :param k: Length of additional character
    :returns: Original filename with additional random string of size k
    """
    filename = filename.split(".", 1)
    salt = "".join(random.choices(string.ascii_lowercase, k=k))
    filename[0] = f"{filename[0]}_{salt}"
    return ".".join(filename)