The problem lies in the interfaces. Components, even when they are independents, expose interfaces. Those interfaces acts as a contract between the component an

The problem lies in the interfaces. Components, even when they are independents, expose interfaces. Those interfaces acts as a contract between the component and its users. Python needs a way to make those interfaces automatically verifiable. It's even worse once you start to use big libraries. If you're using top level functions, then maybe your IDE can help you, but as soon as you're dealing with magical properties or parameters, that becomes a mess. Take for example the "desc" magical function in SQLAlchemy, on things like "order_by" on relationships. That's extremely useful and clever, but i'd really like python to give me some "ok, you're not doing things wrong" message as I'm typing. Even better, once i enter a relationship declaration, it should give me a list of all the parameter i can use, along with the things thoses properties accept for value. This way i wouldn't have to check the documentation every time i'm writing one. It could also let me discover new things as i'm typing ("hey what's that property doing ? that looks interesting..."). Autocompletion is another way of discovering APIs. But for that, you need type declarations. EDIT : as for my api, it's really nothing fancy. It's structured in three big parts "admin / common / public". They each have their "model / business / service" layers, and each have their modules. Only the service layer is impacted by flask. I have some "utils" modules for very low-level stuffs (json serialization, etc). Flask configuration are used a bit everywhere, because i want my api to have only one configuration file. Nothing special, really.