python - sqlalchemy app.config使用报错

#!/usr/bin/python
#coding=utf-8

from flask import Flask
from flask_sqlalchemy import SQLAlchemy


app = Flask(__name__)
db = SQLAlchemy(app)


class News(db.Model):
    """ 新闻模型 """
    __tablename__ = 'news'

    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(200), nullable=False)
    content = db.Column(db.String(2000), nullable=False)
    is_valid = db.Column(db.Boolean, default=True)
    created_at = db.Column(db.DateTime)
    updated_at = db.Column(db.DateTime)

    comments = db.relationship('Comments', backref='news',
                                lazy='dynamic')

    def __repr__(self):
        return '' % self.title


class Comments(db.Model):
    """ 新闻评论 """

    id = db.Column(db.Integer, primary_key=True)
    content = db.Column(db.String(2000), nullable=False)
    is_valid = db.Column(db.Boolean, default=True)
    created_at = db.Column(db.DateTime)
    updated_at = db.Column(db.DateTime)

    new_id = db.Column(db.Integer, db.ForeignKey('news.id'))

    def __repr__(self):
        return '' % self.content


app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://root:123456@127.0.0.1/flask_test'

if __name__ == '__main__':
    app.run(debug=True)
    

打算学习创建数据库的，但是提示报错，

>>> from test_orm import db
D:\mycodes\virtual\flask-test\lib\site-packages\flask_sqlalchemy\__init__.py:819
: UserWarning: SQLALCHEMY_DATABASE_URI not set. Defaulting to "sqlite:///:memory:".
  'SQLALCHEMY_DATABASE_URI not set. Defaulting to '
>>>

我去看了一下源码

if 'SQLALCHEMY_DATABASE_URI' not in app.config:
    warnings.warn(
        'SQLALCHEMY_DATABASE_URI not set. Defaulting to '
        '"sqlite:///:memory:".'
    )
    

上面说。。。SQLALCHEMY_DATABASE_URI不在app.config里面。。。但是我上面的编码。。确实在这个里面。。我崩溃。。。求助大神们。。。哪出错了。。