Flask: 2FA if语句可能由于不同的变量类型而失败？

from flask import Flask, request

app = Flask(__name__)

@app.route('/login', methods=['POST'])
def login():
    username = request.form.get('username')
    password = request.form.get('password')
    verification_code = request.form.get('verification_code')

    # 假设数据库中存储了用户的用户名、密码和验证码
    db_username = 'example_user'
    db_password = 'example_password'
    db_verification_code = '123456'

    if username == db_username and password == db_password:
        if isinstance(verification_code, str) and verification_code == db_verification_code:
            return '登录成功'
        else:
            return '验证码错误'
    else:
        return '用户名或密码错误'

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