13.2 Attribute access

Learning objectives

By the end of this section you should be able to

• Implement a subclass that accesses inherited attributes from the superclass.
• Write a subclass's __init__() that inherits superclass instance attributes and creates new instance attributes.

Creating a simple subclass

Subclasses have access to the attributes inherited from the superclass. When the subclass's __init__() isn't explicitly defined, the superclass's __init__() method is called. Accessing both types of attributes uses the same syntax.

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class SuperClass:
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  def __init__(self):
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    self.feat_1 = 1
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    self.feat_2 = ""
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  def bc_display(self):
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    print(f"Superclass: {self.feat_2}")
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class SubClass(SuperClass):
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  def dc_display(self):
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    print(f"Subclass: {self.feat_2}")
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dc_1 = SubClass()

class SuperClass:
  def __init__(self):
    self.feat_1 = 1
    self.feat_2 = ""

  def bc_display(self):
    print(f"Superclass: {self.feat_2}")

class SubClass(SuperClass):
  def dc_display(self):
    print(f"Subclass: {self.feat_2}")

dc_1 = SubClass()

Using __init__() to create and inherit instance attributes

A programmer often wants a subclass to have new instance attributes as well as those inherited from the superclass. Explicitly defining a subclass's __init__() involves defining instance attributes and assigning instance attributes inherited from the superclass.

    class Employee:
      count = 0
      def __init__(self):
        Employee.count += 1
        self.e_id = Employee.count
        self.hire_year = 2023

      def emp_display(self):
        print(f"Employee {self.e_id} hired in {self.hire_year}")

    class Developer(Employee):
      def __init__(self):
        Employee.count += 1
        self.e_id = Employee.count
        self.hire_year = 2023
        self.lang_xp = ["Python", "C++", "Java"]

      def dev_display(self):
        print(f"Proficient in {self.lang_xp}")
    
    emp_1 = Employee()
    dev_1 = Developer()