def token2sub_tokens(tokenizer, token):
    """
    Take in a string value and use tokenizer to tokenize it into subtokens.
    Return a list of sub tokens.
    """
    res = []
    for sub_token in tokenizer.tokenize(token):
        # make sure it's not an empty string
        if len(sub_token) > 0: 
            res.append(tokenizer.convert_tokens_to_ids(sub_token))
    return res