class MongodbClient:
    def __init__(self,host="127.0.0.1",port=27017,username="",userpwd="",db_name=""):
        self.host = host
        self.port = port
        self.client = pymongo.MongoClient(host=self.host, port=self.port)
        self.db = self.client[db_name]
        self.db.authenticate("root", "root123.",mechanism='SCRAM-SHA-1')

client直接连接mongodb中自己的业务db报错pymongo.errors.OperationFailure: Authentication failed. 

解决办法：

先用密码连接mongo的默认admin库，然后再连接自己的库就可以连接成功访问数据啦

class MongodbClient:
    def __init__(self,host="127.0.0.1",port=27017,username="",userpwd="",db_name=""):
        self.host = host
        self.port = port
        self.client = pymongo.MongoClient(host=self.host, port=self.port)
        # 切换数据库
        self.db = self.client.admin
        self.db.authenticate("root", "root123.", mechanism='SCRAM-SHA-1')
        self.db = self.client[db_name]
if __name__ == '__main__':
    mongo = MongodbClient()
    collection = mongo.db.testuser
    print(collection.find_one({"city": "北京市","startTime":{"$gte":datetime(2023,3,7,0,0,0)}}))