Extend Config type about flask

[davidism]

That's because config is a dict-like interface with arbitrary keys and values, so there's no way to say what an arbitrary key's type is. You can probably write a class that uses attribute access or a TypedDict instead to specify the types of known keys, but that only covers the keys you know about, not the extra ones that extensions or applications may use, which is presumably the interesting ones. But subclassing Config to provide other type information shouldn't require anything from Flask itself. You're welcome to explore this, and if you discover that something in Flask is needed, then please open a specific issue about that.