In case you use Django or Flask (or any Python framework) as your backend for a simple monolithic application where the front-end and backend are tightly coupled, jinja templates would make the job easier for you because you can take advantage of template variables passed on from the backend.

But as Luis pointed out, it would be better to follow a RESTful approach to build applications. You could use a micro-framework like Flask or Pyramid to serve the REST endpoints and use a front-end framework like React/Angular that interacts with the backend service. This way, if you have to build a whole new client (like a mobile or desktop app), it could still interact with your existing backend service. When you build a RESTful service, if the application might turn out huge/complex later, it would be good to follow API versioning right from the start. Here are some best practices on building RESTful services.

Assuming you mean frontend web development.

It depends on the type of project, but I'd recommend following a REST server-client architecture whenever possible, which makes separating the client from the data logic easier.

With that in mind, then the difference depends on the type of application:

• If it's an SPA, then the client could be any of the JS frameworks (or just vanilla js is it's not too complex), it'd consume the REST API written in python.
• If it isn't, then the client could be written in python itself, with any of the templating languages available. Jinja is the one I use most often.

Sometimes, the type of application allows for enough logic to live on the REST API to make the decision one of what templates to use JS or Python.

Depends on the platform. Desktop, web, etc.