RuntimeError: The session is unavailable because no secret key was set. Set the secret_key on the application to something unique and secret.
解决办法是
app = Flask(__name__)
app.config['SECRET_KEY'] = ''
session 必须带有['SECRET_KEY'] ,可以随机写一个,也可以自己使用python自带生成随机数模块,生成一个写上。