# Object Oriented Programming

Chapter 17.

## Key ideas

### From chapter 17

• An instance of a class is mutable.
• A mutator method is a method of a class that changes the values of one or more instance variables.
• Shallow equality occurs when two variables refer to the same object in the computer’s memory. The Python keyword is tests for shallow equality.
• Deep equality occurs when either there is shallow equality OR two variables refer to objects that contain the same underlying (significant) values.
• The method __add__(self, other) can be defined so that the operator + can be used.