[Fixed]-How can I create an API for my web app and the mobile version of that web app in python?

An API does not care if the client that sends the requests is a mobile app or browser (unless of course you send and use the information on purpose). For example if your API exposes the “www.myapp.com/registeruser/” URL and requires a POST with username and password, you can call this URL with those parameters from any client that is able to send that.

If what you want is use the same client-side code for both desktop and mobile (trying to understand what you need!), you can look at responsive websites. A package like django-bootstrap3 works very well with Django and is easy to use.

If your goal is to develop a native mobile application that will consume your API, then you can use Django REST framework to add API endpoint to your current Django application. One possibility is that you will have another file added in every app of your Django project, and it is serializers.py (at the same level as models.py).