pymongo.errors.ConfigurationError: The DNS query name does not exist:

I am trying to connect to mongo db from flask virtual env. But I'm getting this error pymongo.errors.ConfigurationError: The DNS query name does not exist: version python = 3.7 dnspython = 2.2.1

def establish_connection():
    app = flask.Flask(__name__)
    connection_string = "mongodb+srv://username:password@clustername.mongodb.net/?retryWrites=true&w=majority"
    app.config["MONGO_URI"] = connection_string
    mongodb_client = PyMongo(app)