.. include:: <s5defs.txt>
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Object-Orientation
==================

What is an Object?
==================

An object consist of two elements:

 - State + Behaviour


Why Object-Orientation?
=======================

Abstraction: To use an object, we don't need to know, how it is implemented.


Object-Orientation in Dynamic Languages
=======================================

Two important principles for OO in dynamic languages:

 1. Everything is an object
 2. Every object has a type

Python: Instance-Attributes
===========================

 - Instance-attributes are the state part of an object
 - they are stored in a dictionary attached to the instance

Python: Object Creation
=======================

 - instances are created by calling a type
 - classes are normal instances of type ``type``

Messages
========

 - Objects interact by sending messages to each other
 - The implementation of a message is called a method
 - message send consists of two steps: *lookup* and *call*
 - lookup finds which method to use, call calls it
 - lookup happens fully at runtime!