title: declaring empty class member in python
body: <p>i am trying to read a tree structure file in python. 
  I created a class to hold the tree objects. One of the members
  should hold the parent object. 
  Since the parentObject member is of the same type as the class itself,
  I need to declare this as an empty variable of type "self". </p>
  
  <p>How do I do that in python?</p>
  
  <p>Thank you very much for your help.  </p>