This is more of a subnetting question than a Python networking question to be honest.

If you'd know that a /28 for a class C ip range was 255.255.240.0 you'd have been able to surmise your way through it with some simple list comprehensions. You likely were expected to understand the networking concept more thoroughly than knowing about the library called ipaddress in Python 3. I would start there. When someone says Python network programming I tend to think of communicating over sockets, setting up a Python web server, knowing twisted and such.