OOP Pillars (Encapsulation, and how Python is not good on that).

encapsulation.cpp

/* C++ demonstration of OOP Encapsulation principle. */

#include <iostream>

using namespace std;

class Car {
  public:
    int number_of_wheels = 0;
    int door_angle_opening_degrees = 85;
  protected:
    string safe_belt_material = "polyester";
  private:
    int taillights = 2;
    int rearlights = 2;
};

class Ferrari: public Car {

    public:
        void info() {
            number_of_wheels = 4;
            door_angle_opening_degrees = 90;
            cout << "Number or Wheels:             " << number_of_wheels << endl;
            cout << "Door angle opening (degrees): " << door_angle_opening_degrees << endl;
            cout << "Safe Belt material:           " << safe_belt_material << endl;
        };

        void default_car_info() {
            // This function will stop program compilation,
            // for it's trying to access Private members from Car class.
            cout << "Tailights:  " << taillights << endl;
            cout << "Rearlights: " << rearlights << endl;
        }

};

int main()
{   
    Ferrari ferrari;
    ferrari.info();
    // Protected members are only accessible inside the Class and Subclasses.}
    // Again, this code will not compile...
    cout << "Safe belt material: " << ferrari.safe_belt_material << endl;

    return 0;
}

encapsulation_compile.sh

g++ -o encapsulation encapsulation.cpp

# encapsulation.cpp: In member function ‘void Ferrari::default_car_info()’:
# encapsulation.cpp:30:39: error: ‘int Car::taillights’ is private within this context
#    30 |             cout << "Tailights:  " << taillights << endl;
#       |                                       ^~~~~~~~~~
# encapsulation.cpp:12:9: note: declared private here
#    12 |     int taillights = 2;
#       |         ^~~~~~~~~~
# encapsulation.cpp:31:39: error: ‘int Car::rearlights’ is private within this context
#    31 |             cout << "Rearlights: " << rearlights << endl;
#       |                                       ^~~~~~~~~~
# encapsulation.cpp:13:9: note: declared private here
#    13 |     int rearlights = 2;
#       |         ^~~~~~~~~~
# encapsulation.cpp: In function ‘int main()’:
# encapsulation.cpp:42:47: error: ‘std::string Car::safe_belt_material’ is protected within this context
#    42 |     cout << "Safe belt material: " << ferrari.safe_belt_material << endl;
#       |                                               ^~~~~~~~~~~~~~~~~~
# encapsulation.cpp:10:12: note: declared protected here
#    10 |     string safe_belt_material = "polyester";
#       |            ^~~~~~~~~~~~~~~~~~

encapsulation_python.py

class Car:

    # Public
    number_of_wheels = 0
    door_angle_opening_degrees = 85
    # Protected
    _safe_belt_material = "polyester"
    # Private
    __tail_lights = 2
    __rear_lights = 2


class Ferrari(Car):

    def info(self):
        print("Number or Wheels (before):     ", Car.number_of_wheels)
        Car.number_of_wheels = 4;
        print("Number or Wheels (after):      ", Car.number_of_wheels)
        print("Door angle opening (before):   ", Car.door_angle_opening_degrees)
        Car.door_angle_opening_degrees = 90;
        print("Door angle opening (after):    ", Car.door_angle_opening_degrees)
        # Protected members are only accesible inside Classes and their Subclasses !!!
        print("Safe Belt material (before):   ", Car._safe_belt_material)
        Car._safe_belt_material = "viscose"
        print("Safe Belt material (after):    ", Car._safe_belt_material)
        # These Private members are only accesible inside Classes !!!
        print("Number of Taillights (before): ", Car._Car__tail_lights)
        print("Number of Rearlights (before): ", Car._Car__rear_lights)
        Car._Car__tail_lights = 4
        Car._Car__rear_lights = 4
        print("Number of Taillights (after): ", Car._Car__tail_lights)
        print("Number of Rearlights (after): ", Car._Car__rear_lights)


fer = Ferrari()
fer.info()
# Protected member being accessed outside Class and their Subclasses...
print("Safe belt material: ", fer._safe_belt_material)
# Again, Private members being accessed outside their Class!!!
print("Tail lights: ", fer._Car__tail_lights)
print("Rear lights: ", fer._Car__rear_lights)


# $ python3 encapsulation.py
# Number or Wheels (before):      0
# Number or Wheels (after):       4
# Door angle opening (before):    85
# Door angle opening (after):     90
# Safe Belt material (before):    polyester
# Safe Belt material (after):     viscose
# Number of Taillights (before):  2
# Number of Rearlights (before):  2
# Number of Taillights (after):  4
# Number of Rearlights (after):  4
# Tail lights:  4
# Rear lights:  4