OO-programming question

[Ing. Roman Fischer]

Reading "Learning Python" I have problems of understanding the advantages of
the concept of object-oriented programming in Python:

1. When I understand it wright I can add/delete items to classes AND to
object AFTER their definition. What is the advantage of this concept? I
think it destroys the possibillity to know what a  class or object consists
of. 

2. In Java and Visual Basic there is the concept of interfaces (a definition
of what a class must have included when implementing the interface). Is
there anything like that in Python?

3. In Java there is the concept of abstract classes (a class that have a lot
of definitions (e.g. methods) but not all is really implemented, so a
derived class has to implement). Is there anything like that in Python?

4. How do I find out to which class(es) an object belongs to?

5. What is the advantage of including "self" into the paramters of a method?

Thanks in advance

Roman Fischer