from bs4 import BeautifulSoup
import requests, pymongo

#激活MongoDB
client = pymongo.MongoClient('localhost', 27017)
#给数据库命名
xiaozhu = client['xiaozhu']
#创建一个表单
bnb_info = xiaozhu['bnb_info']

#定义一个能获取多页信息的函数
def getMorePage(pages):
    for page in range(1, pages+1):
        url = 'http://bj.xiaozhu.com/search-duanzufang-p{}-0/'
        wb_data = requests.get(url.format(page))
        soup = BeautifulSoup(wb_data.text, 'html.parser')

        #房子标题、价格
        titles = soup.select("span.result_title")
        prices = soup.select("span.result_price > i")

        # 打包存入字典
        for title, price in zip(titles, prices):
            data = {
                    'title':title.get_text(),
                    'price':price.get_text()
            }
            #将数据写入数据库==填写Excel表格每一行
            bnb_info,insert_one(data)
    print("完成")
getMorePage(3)

# 从数据库中筛选信息
for i in bnb_info.find():
    if i['price'] >= 500: 
    #筛选出价格大于等于500的信息
        print(i)
#上诉代码也可写成
for i in bnb_info({'price':{'$gte':500}}):
    print(i)

补充：

$lt less than <

$lte less than equal <=

$gt greater than >

$gte …… >=

$ne not than !=