Get an extension from the given path name. If an extension cannot be found,
    it will return an empty string

def get_ext(path_name, *, if_all_ext=False):
    """
    Get an extension from the given path name. If an extension cannot be found,
    it will return an empty string
    """
    if has_ext(path_name):
        return os.path.splitext(path_name)[EXTENSION]
    elif if_all_ext and has_ext(path_name, if_all_ext=True):
        return os.path.splitext(path_name)[NAME]
    else:
        return ''