Can I use an object (an instance of a class) as a dictionary key in Python?

I want to use a class instance as a dictionary key, like:

classinstance = class()
dictionary[classinstance] = 'hello world'

Python seems to be not able to handle classes as dictionary key, or am I wrong? In addition, I could use a Tuple-list like [(classinstance, helloworld),...] instead of a dictionary, but that looks very unprofessional. Do you have any clue for fixing that issue?