我想匹配文本中的字符串（n-gram），并使用一種方法來獲得偏移量：string_to_match = "many workers are very underpaid"  text = "The new york times claimed in a report that many workers are very underpaid in some africans countries."所以結果我想得到一個像這樣的元組("matched", 44, 75)，其中 44 是開始，75 是結束。這是我構建的代碼，但它僅適用于 unigram。def extract_offsets(line, _len=len):    words = line.split()    index = line.index    offsets = []    append = offsets.append    running_offset = 0    for word in words:        word_offset = index(word, running_offset)        word_len = _len(word)        running_offset = word_offset + word_len        append(("matched", word_offset, running_offset - 1))    return offsetsdef get_entities(offsets):    entities = []    for elm in offsets:        if elm[0] == "string_to_match": # here string_to_match is only one word            entities.append(elm)    return entitiesoffsets = extract_offsets(text)entities = get_entities(offsets) # [("matched", start, end)]任何使之適用于字符串序列或 n-gram 的提示！