Mongodb缓存爬虫数据

from pymongo import MongoClient
from datetime import datetime,timedelta
import zlib
import pickle

class MongoCache:
    def __init__(self,client=None,expires=timedelta(days=30)):
        self.client=MongoClient('localhost',27017)
        self.db=client['cache']                 #新建数据库
        '''Mongodb不需要创建表，会自动创建'''
        self.db.webpage.create_index('timestamp',
                                     expireAfterSeconds=expires.total_seconds())
    
    def __getitem__(self, item):
        record=self.db.webpage.find_one({'_id':item})
        if record:
            return pickle.loads(zlib.decompress(record['result']))
        else:
            raise KeyError(item+' dose not exist!')
    
    def __setitem__(self, key, value):
        record={'result':zlib.compress(pickle.dumps(value)),'timestamp':datetime.utcnow()}
        self.db.webpage.update({'_id':key},{'$set':record},upset=True)