def METHOD_NAME(x):
    """Turn a path name into an identifier we can use as a file name.
    Take into account that it may contain characters we want to remove,
    that the full path may be too long to use as a file name, and that
    it needs to remain unique.
    """
    x = re.sub(r'[^a-zA-Z0-9_-]', '', x)
    return x[-20:] + md5digest(x)