I would recommend either showing the class definitions or allowing the challengers to create the classes themselves.

What about the useless Triangle?

Not a suggestion.

there is no... point (!) to use a class Point in python if the represented points are only coordinates, without additional behaviors/properties. Python has already a structure for that: tuples.

I felt awkward kludging this together. If we're going to all the trouble to make Triangles class objects, why don't we write a method so each Triangle knows its own perimeter and area? Then you could just return Triangle.perimeter() ...