13.4 Hierarchical inheritance

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.

Implementing hierarchical inheritance

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

Example 1 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

Note

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)

Note

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

# Define Instrument class

# Define Woodwind class

# Define String class

print(f"This flute belongs to {flute_1.owner} and is made of {flute_1.material}")
print(f"This cello belongs to {cello_1.owner} and has {cello_1.num_strings} strings")