My friend said, "Pylons is so much better for web services."
My other friend said, "You can modify Django in a way to do exactly whatever you like."
In Django, what is necessary to be modified (urls.py? models classes? settings?) in order to do "web services" with APIs and REST and versioning, etc etc.?
Yes Django can be used for web services. Check out django-piston:
A mini-framework for Django for creating RESTful APIs.
Piston is a relatively small Django application that lets you create application programming interfaces (API) for your sites.
Yes, we use it directly. We have view functions that respond to some URI's with serialized JSON or XML objects instead of pretty HTML pages.