flask全局变量错误

from flask import Flask, g

app = Flask(__name__)

@app.before_request
def before_request():
    g.db = connect_to_database()

@app.teardown_request
def teardown_request(exception):
    db = getattr(g, 'db', None)
    if db is not None:
        db.close()

@app.route('/')
def index():
    # 使用g.db进行数据库操作
    return "Hello, World!"

from flask import Flask, session

app = Flask(__name__)
app.secret_key = 'your_secret_key'

@app.route('/login')
def login():
    session['username'] = 'example_user'
    return "Logged in."

@app.route('/logout')
def logout():
    session.pop('username', None)
    return "Logged out."

@app.route('/')
def index():
    username = session.get('username')
    return f"Hello, {username}!" if username else "Hello, Guest!"