Master Python Encapsulation & Inheritance: Public vs Private Variables Explained

Encapsulation: Hiding Information

Encapsulation in object-oriented programming restricts direct access to an object’s data and methods, allowing the internal representation to be hidden from the outside.

Public Instance Variables

In Python a public instance variable can be created in the constructor:

class Person:
    def __init__(self, first_name):
        self.first_name = first_name

raymond = Person('Raymond')
print(raymond.first_name)  # => Raymond

A class attribute can also be defined directly in the class body:

class Person:
    first_name = 'Raymond'

ex = Person()
print(ex.first_name)  # => Raymond

Public variables can be reassigned simply by assigning a new value:

ex = Person('Raymond')
ex.first_name = 'Jason'
print(ex.first_name)  # => Jason

Non-Public Instance Variables

Python has no true private attributes, but a leading underscore is the convention for non-public members.

class Person:
    def __init__(self, first_name, email):
        self.first_name = first_name
        self._email = email

ex = Person('raymond', '[email protected]')
print(ex._email)  # => [email protected]

Typical getter and setter methods are used to access and modify such attributes:

class Person:
    def __init__(self, first_name, email):
        self.first_name = first_name
        self._email = email

    def email(self):
        return self._email

    def update_email(self, new_email):
        self._email = new_email

ex = Person('raymond', '[email protected]')
print(ex.email())          # => [email protected]
ex.update_email('[email protected]')
print(ex.email())          # => [email protected]

Public Methods

class Person:
    def __init__(self, first_name, age):
        self.first_name = first_name
        self._age = age

    def show_age(self):
        return self._age

raymond = Person('Raymond', 38)
print(raymond.show_age())  # => 38

Non-Public Methods

class Person:
    def __init__(self, first_name, age):
        self.first_name = first_name
        self._age = age

    def _show_age(self):
        return self._age

raymond = Person('Raymond', 38)
print(raymond._show_age())  # => 38

Another pattern uses a public method that calls a non-public helper:

class Person:
    def __init__(self, first_name, age):
        self.first_name = first_name
        self._age = age

    def show_age(self):
        return self._get_age()

    def _get_age(self):
        return self._age

raymond = Person('Raymond', 38)
print(raymond.show_age())  # => 38

Inheritance: Sharing Behavior and Features

Classes can inherit attributes and methods from a parent class.

class Car:
    def __init__(self, number_of_wheels, seating_capacity, maximum_velocity):
        self.number_of_wheels = number_of_wheels
        self.seating_capacity = seating_capacity
        self.maximum_velocity = maximum_velocity

my_car = Car(4, 5, 250)
print(my_car.number_of_wheels)      # => 4
print(my_car.seating_capacity)      # => 5
print(my_car.maximum_velocity)     # => 250

A subclass can reuse the parent’s implementation without redefining it:

class ElectricCar(Car):
    def __init__(self, number_of_wheels, seating_capacity, maximum_velocity):
        Car.__init__(self, number_of_wheels, seating_capacity, maximum_velocity)

my_electric_car = ElectricCar(4, 5, 250)
print(my_electric_car.number_of_wheels)      # => 4
print(my_electric_car.seating_capacity)      # => 5
print(my_electric_car.maximum_velocity)     # => 250

Summary

How Python variables work

How conditional statements work

How loops work

Using lists and sorting

Dictionary key-value structures

Iterating over data structures

Objects and classes

Attributes as object data

Methods as object behavior

Setting and getting attributes in Python

Encapsulation: hiding information

Inheritance: sharing behavior and features

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