problem with recursive container printing

I am working on a Prothon bug relating to printing out containers that are
recursive, i.e. contain themselves directly or indirectly, and I checked to
see how Python handles it.  I was dissapointed to see how wimpy Python is
when it comes to printing containers at all.  Instances are not first class
objects apparently:

    class K:
          def __str__(self):
                return 'hello world'

    k = K()
    print k         # hello world
    print [k]      # [<__main__.K instance at 0x008F9968>]

Prothon would print ['hello world'] of course.  Does anyone know why they do
this?  Do you think it is to solve the recursive printing problem that I am
chasing right now?