倒排索引是一种检索方式，比如存入数据库的数据是存一篇文章进去，然而检索时我们经常需要通过关键词检索，所以提前做好倒排索引即可方便检索，而省略掉全表扫描的问题了，这是一种用空间换时间的方法。

使用字典构造倒排索引

sentences = ['This is the first word',
             'This is the second text Hello How are you',
             'This is the third, this is it now']
sentence_dict = {}
index_dict = {}
for index, line in enumerate(sentences):
    line = line.lower()  # 小写
    sentence_dict[index] = line
    for char in line.split(' '):
        if not char.strip():
            continue
        if char in index_dict:
            index_dict[char].add(index)
        else:
            index_dict[char] = {index}

检索

检索时依次遍历每一个待检索的单词对应的文章列表，然后取它们的交集即可，交集意味着这个文章包含待检索的全部单词。

def list_intersection(list1: list, list2: list) -> list:  # 取交集
    return list(set(list1).intersection(set(list2)))


index_value = list(sentence_dict.keys())
search_key = ['this', 'first']
for key in search_key:
    index_value = list_intersection(index_dict[key], index_value)
print(index_value)

完整代码

sentences = ['This is the first word',
             'This is the second text Hello How are you',
             'This is the third, this is it now']
sentence_dict = {}
index_dict = {}
for index, line in enumerate(sentences):
    line = line.lower()  # 小写
    sentence_dict[index] = line
    for char in line.split(' '):
        if not char.strip():
            continue
        if char in index_dict:
            index_dict[char].add(index)
        else:
            index_dict[char] = {index}


# 检索时
def list_intersection(list1: list, list2: list) -> list:  # 取交集
    return list(set(list1).intersection(set(list2)))


index_value = list(sentence_dict.keys())
search_key = ['this', 'first']
for key in search_key:
    index_value = list_intersection(index_dict[key], index_value)
print(index_value)