Inheritance

• Inheritance: allows for an object type to inherit features from another object type
• Reusability: Inheritance avoids having to rewrite much of the same code
• Maintenance: Code is easier to maintain. Changes in one part of a class are immediately implemented in other parts of a class

Derived Classes

• Define a general class (Base Class)
• Define specialised classes (Derived Classes) with unique features

Inheritance Syntax

• Syntax for a derived class definition:

class DerivedClassName(BaseClassName):
	pass

• The name BaseClassName must be defined in a scope containing the derived class definition

e.g.

# base or parent class
class Device:
	pass

# derived or child class
class Emitter(Device):
	pass

# derived or child class
class Sensor(Device):
	pass

Execution of Derived and Base Classes

• When a Derived Class Object is constructed, any base class inherited is remembered
• Execution of a derived class definition proceeds the same as for a base class
• If a requested attribute is not found in a class:
  • the search proceeds to look in the Base Class (if specified)
  • and occurs recursively if the Base Class itself is derived from some other class
• Derived Classes may override methods of their Base Classes

Inheritance Example I

• To inherit: do not list the method in the derived class
  • e.g. move()
• To redefine (override): write the method in the derived class using the same name in the base class
  • e.g. __init__(), __str__()
• to add a new attribute or method: code them in as you would in any class
  • e.g. width, height, area(), circum()