How to use the pythainlp.util.isthai function in pythainlp

def _doc2features(doc, i) -> dict:
    word = doc[i][0]
    postag = doc[i][1]

    # Features from current word
    features = {
        "word.word": word,
        "word.stopword": _is_stopword(word),
        "word.isthai": isthai(word),
        "word.isspace": word.isspace(),
        "postag": postag,
        "word.isdigit": word.isdigit(),
    }
    if word.isdigit() and len(word) == 5:
        features["word.islen5"] = True

    # Features from previous word
    if i > 0:
        prevword = doc[i - 1][0]
        prevpostag = doc[i - 1][1]
        prev_features = {
            "word.prevword": prevword,
            "word.previsspace": prevword.isspace(),
            "word.previsthai": isthai(prevword),
            "word.prevstopword": _is_stopword(prevword),

"word.isthai": isthai(word),
        "word.isspace": word.isspace(),
        "postag": postag,
        "word.isdigit": word.isdigit(),
    }
    if word.isdigit() and len(word) == 5:
        features["word.islen5"] = True

    # Features from previous word
    if i > 0:
        prevword = doc[i - 1][0]
        prevpostag = doc[i - 1][1]
        prev_features = {
            "word.prevword": prevword,
            "word.previsspace": prevword.isspace(),
            "word.previsthai": isthai(prevword),
            "word.prevstopword": _is_stopword(prevword),
            "word.prevpostag": prevpostag,
            "word.prevwordisdigit": prevword.isdigit(),
        }
        features.update(prev_features)
    else:
        features["BOS"] = True  # Special "Beginning of Sequence" tag

    # Features from next word
    if i < len(doc) - 1:
        nextword = doc[i + 1][0]
        nextpostag = doc[i + 1][1]
        next_features = {
            "word.nextword": nextword,
            "word.nextisspace": nextword.isspace(),
            "word.nextpostag": nextpostag,

"word.prevpostag": prevpostag,
            "word.prevwordisdigit": prevword.isdigit(),
        }
        features.update(prev_features)
    else:
        features["BOS"] = True  # Special "Beginning of Sequence" tag

    # Features from next word
    if i < len(doc) - 1:
        nextword = doc[i + 1][0]
        nextpostag = doc[i + 1][1]
        next_features = {
            "word.nextword": nextword,
            "word.nextisspace": nextword.isspace(),
            "word.nextpostag": nextpostag,
            "word.nextisthai": isthai(nextword),
            "word.nextstopword": _is_stopword(nextword),
            "word.nextwordisdigit": nextword.isdigit(),
        }
        features.update(next_features)
    else:
        features["EOS"] = True  # Special "End of Sequence" tag

    return features