How to define a class attribute with no default value in python

I'm a C# developer learning python.

If I want to define a class with certain attributes, but not provide default values for the attributes, how is that done?

For example (this is my best guess of how to do it):

class Spam
    eggs = None
    cheese = None

Or, is this legal:

class Spam
    eggs
    cheese

Or something else?