13.1: Inheritance Basics
- Page ID
- 117606
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- Identify is-a and has-a relationships between classes.
- Differentiate between a subclass and a superclass.
- Create a superclass, subclass, and instances of each.
is-a vs has-a relationships
Classes are related to each other. An is-a relationship exists between a subclass and a superclass. Ex: A daffodil is a plant. A Daffodil
class inherits from a superclass, Plant
.
Is-a relationships can be confused with has-a relationships. A has-a relationship exists between a class that contains another class. Ex: An employee has a company-issued laptop. Note: The laptop is not an employee.
Inheritance in Python
Inheritance uses an is-a relationship to inherit a class from a superclass. The subclass inherits all the superclass's attributes and methods, and extends the superclass's functionality.
In Python, a subclass is created by including the superclass name in parentheses at the top of the subclass's definition:
class SuperClass:
# SuperClass attributes and methods
class SubClass(SuperClass):
# SubClass attributes and methods
class Daisy(Plant):
class Daisy:
class Plant:
Python documentation for inheritance uses multiple terms to refer to the class that is inherited from and the class that inherits. This book uses superclass/subclass throughout for consistency.
Class inherited from | Class that inherits |
---|---|
superclass | subclass |
base class | derived class |
parent class | child class |
Given the Employee
class, create a Developer
class that inherits from Employee
. The Developer
class has one method, update_codebase()
, which prints "Employee has updated the codebase"
. Then, use the Developer
instance, python_dev
, to call print_company()
and update_codebase()
.
Define three classes: Polygon
, Rectangle
, and Square
:
Polygon
has the methodp_disp()
, which prints"object is a Polygon"
.Rectangle
inherits fromPolygon
and has the methodr_disp()
, which prints"object is a Rectangle"
.Square
inherits fromRectangle
and has the methods_disp()
, which prints"object is a Square"
.
Create an instance of each class. Then, for each instance, call all the methods the instance has access to.