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13.4: Hierarchical Inheritance

Last updated

Mar 30, 2025
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- 13.3: Methods
- 13.5: Multiple Inheritance and Mixin Classes

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Learning Objectives

By the end of this section you should be able to

Label relationships between classes as types of inheritance.
Construct classes that form hierarchical inheritance.

Hierarchical inheritance basics

Hierarchical inheritance is a type of inheritance in which multiple classes inherit from a single superclass. Multilevel inheritance is a type of inheritance in which a subclass becomes the superclass for another class. Combining hierarchical and multilevel inheritance creates a tree-like organization of classes.

Checkpoint: Hierarchical organization and types of inheritance

Access multimedia content

Concepts in Practice: Hierarchical organization

Which is an example of hierarchical inheritance?

Class B inherits from Class A
Class C inherits from Class A

Class B inherits from Class A
Class C inherits from Class B

Class B inherits from Class A
Class C inherits from Class D

Which group of classes is hierarchical inheritance appropriate for?

Cat, Dog, Bird
Employee, Developer, SalesRep
Dessert, BakedGood, ApplePie

Implementing hierarchical inheritance

Multiple classes can inherit from a single class by simply including the superclass name in each subclass definition.

Example 13.4

Choir members

    class ChoirMember:
      def display(self):
        print("Current choir member")

    class Soprano(ChoirMember):
      def display(self):
        super().display()
        print("Part: Soprano")

    class Soprano1(Soprano):
      def display(self):
        super().display()
        print("Division: Soprano 1")

    class Alto(ChoirMember):
      def display(self):
        super().display()
        print("Part: Alto")

    class Tenor(ChoirMember):
      def display(self):
        super().display()
        print("Part: Tenor")

    class Bass(ChoirMember):
      def display(self):
        super().display()
        print("Part: Bass")

    mem_10 = Alto()
    mem_13 = Tenor()
    mem_15 = Soprano1()

    mem_10.display()
    print()
    mem_13.display()
    print()
    mem_15.display()

The code's output is:

    Current choir member
    Part: Alto

    Current choir member
    Part: Tenor

    Current choir member
    Part: Soprano
    Division: Soprano 1

Concepts in Practice: Implementing hierarchical inheritance

Consider the program:

    class A:
      def __init__(self, a_attr=0):
        self.a_attr = a_attr

    class B(A):
      def __init__(self, a_attr=0, b_attr=0):
        super().__init__(a_attr)
        self.b_attr = b_attr

    class C(A):
      def __init__(self, a_attr=0, c_attr=0):
        super().__init__(a_attr)
        self.c_attr = c_attr

    class D(B):
      def __init__(self, a_attr=0, b_attr=0, d_attr=0):
        super().__init__(a_attr, b_attr)
        self.d_attr = d_attr
    
    b_inst = B(2)
    c_inst = C(c_attr=4)
    d_inst = D(6, 7)

What is the value of b_inst.b_attr?

2

Error

Which attributes does c_inst have access to?

a_attr
a_attr, c_attr
c_attr

Which attributes does d_inst have access to?

b_attr, d_attr
a_attr, b_attr, d_attr
d_attr

Try It: Overriding methods

Define three classes: Instrument, Woodwind, and String.

Instrument has instance attribute owner, with default value of "unknown".
Woodwind inherits from Instrument and has instance attribute material with default value of "wood".
String inherits from Instrument and has instance attribute num_strings, with default value of 4.

The output should match:

    This flute belongs to unknown and is made of silver
    This cello belongs to Bea and has 4 strings