Flask? Maybe FastAPI.
Even when I'm not using FastAPI now, I use Pydantic everywhere. Types in Python, while not nearly as useful as in a strongly typed language, are a dream come true.
The only gripe I have with Pydantic is that sometimes it has really opinionated type coercion that can get you in trouble sometimes. For instance, `Union[int, float]` will accept either an int or a float, sure, but it will always output an int. This isn't difficult to fix but may only realize it after having shot yourself in the foot.
Either is good if what you are building is something small and very focused or if you already know exactly what you want to build and want to have freedom making decisions about most aspects of the application.
But if you don't know yet what the product will be, a battery included framework like Django is very nice to get out the door quickly without having to worry too much how to structure the code, what library to use for x, etc.
Also, I think that Django is a good choice over Flask if you've never done anything in flask. But if you have an existing Flask site that can serve as a skeleton, I think it's just as good as Django as a starting point; details such as code structure and common library choice is then already handles - in fact just following https://blog.miguelgrinberg.com/post/the-flask-mega-tutorial... will get you a lot of this too; Do you have any other batteries in mind? Ialso see Django having plenty "gotchas" (although it maybe have changed since I last used it). I definitely much prefer SQLAlchemy over DjangoORM.
But you need to spent at least once quite significant time following mega-tutorials, thinking about how to structure your application, what libraries to use for x, how to integrate them etc.
If you do that, it's great. But what I have seen in practice in various large flask app developed over years is, that in the very beginning people just jump in hacking away because it is so simple, just an app.py and a requirements.txt. Then over time they slap on the same thing Django has, but in a much less robust, hard to maintainable way. I'm guilty of the same, often simply not having time due to reality to really think things trough (the mega tutorial and similar didn't exist when I last started a Flask app).