How to have different py files to handle different routes?
In my experience with flask, you cannot declare route configurations in a central file. Route handling is done via the use of route declarations. In my experience with python frameworks route handling is done at a more granular function level rather than a file level. Even in the frameworks that do have a more central route configuration setup, the routes are defined as being tied to a specific view/controller function not simply a python file. 
As stated, each framework handles it differently. The three frameworks I have looked at in any detail, django, pyramid, and flask, all handle it differently. The closest to what you are looking for is django which has a urls.py file that you place all of your url configurations in, but again it points to function level items, not higher level .py files. Pyramid does a mix with part of a url declaration being put into the __init__.py file of the main module and the use of a decorator to correlate that named route to a function. And then you have flask, which you mentioned having looked at, which appears to use just decorators for "simplicity sake" as they are trying to reduce the number of overall files and configuration files that need to be used or edited to get an application from concept into served space.
I have been studying python for quite sometime now and very recently I decided to get into learning web development side of things. I have experience with PHP and PHP frameworks, along with ruby, where:

Routes are defined in a (single) file and then in that file, each route is assigned to a model (py file) which will uniquely handle incoming requests matching that route.

How can I achieve this with flask AND webapp2?
I read the documentation and tutorial in full but it got me very confused. I just want A file where all routes and how should they be handled are set, and then each route request to be handled by its own model (python file).
All the examples lead to single file apps.
Thank you VERY MUCH, really. Please teach, kindly, in a simple way.