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== 13.1#h(0.6em)Inheritance basics


  
    
=== Learning objectives


    By the end of this section you should be able to


    - 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.


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[is-a relationship between Employee and Developer]


      #link("https://www.openstax.org/r/is-a-relationship")[Is-a relationship between Employee and Developer; ch 13, video 1]
]


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Relationships between classes]
]


  
  
    
=== 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
    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Using inheritance to create subclasses]


      #link("https://www.openstax.org/r/inheritance-subclasses")[Using inheritance to create subclasses; ch 13, video 2]
]


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Creating subclasses]
]


    #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Alternative inheritance terms]


      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.


      #figure(table(
  columns: 2, align: left, inset: 6pt,
  table.header([Class inherited from], [Class that inherits]),
  [superclass], [subclass],
  [base class], [derived class],
  [parent class], [child class],
))
]


  
  #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Employee and Developer classes]


    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().


    class Employee():
    def print\_company(self):
        print("Employee works at Stark Industries")

\# Define Developer class

python\_dev = Developer()
\# Call Employee and Developer methods
]


  #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[
#emph[Polygon classes]


    Define three classes: Polygon, Rectangle, and Square:


    - Polygon has the method p\_disp(), which prints "object is a Polygon".
- Rectangle inherits from Polygon and has the method r\_disp(), which prints "object is a Rectangle".
- Square inherits from Rectangle and has the method s\_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.


    \# Define classes

\# Create instances of Polygon, Rectangle, and Square
\# Call accessible methods
]