Solution for Assignment "Car registration"

car-registration-assignment-solution.py

## Note: del b doesn't call __del__, because it's not guaranteed. Probably because there's a still reference to it in the _registered_cars dictionary 
import re
from enum import Enum, auto


class REGISTRATION_STATUS(Enum):
    SUCCESS = auto()
    INVALID_NUMBER = auto()
    ALREADY_REGISTERED = auto()
    NUMBER_CHANGED = auto()


class TEXT:
    CAR_LIST_PREFIX = 'Registered cars: '
    NO_REGISTERED_CARS = 'There are no registered cars at this moment'
    STATUS = {
        REGISTRATION_STATUS.SUCCESS: 'Successfully registered',
        REGISTRATION_STATUS.NUMBER_CHANGED: 'The car has already number assigned',
        REGISTRATION_STATUS.INVALID_NUMBER: 'Not valid number',
        REGISTRATION_STATUS.ALREADY_REGISTERED: 'Already registered number'
    }


CAR_NUMBER_REGEXP = re.compile('^[A-Z]{3}-[0-9]{3}$')


class Car:
    _registered_cars = {}

    def _is_registered(self):
        return self._car_number in self._registered_cars and self._registered_cars[self.car_number] is self

    def _register(self, car_number):
        if not self._is_registered():
            if car_number not in self._registered_cars:
                self._registered_cars[car_number] = self
                self._registration_status = REGISTRATION_STATUS.SUCCESS
                self._car_number = car_number
            else:
                self._registration_status = REGISTRATION_STATUS.ALREADY_REGISTERED
        else:
            self._registration_status = REGISTRATION_STATUS.ALREADY_REGISTERED

    def __init__(self, car_number=None):
        self._car_number = None
        self._registration_status = None
        if car_number:
            self.car_number = car_number

    @property
    def car_number(self):
        return self._car_number

    @car_number.setter
    def car_number(self, car_number):
        if not CAR_NUMBER_REGEXP.match(car_number):
            self._registration_status = REGISTRATION_STATUS.INVALID_NUMBER
            return

        if self._is_registered() and car_number != self._car_number:
            self._registration_status = REGISTRATION_STATUS.NUMBER_CHANGED
            return

        self._register(car_number)

    @property
    def registered_cars(self):
        car_numbers = list(self._registered_cars.keys())
        return f"{TEXT.CAR_LIST_PREFIX}{', '.join(car_numbers)}" if car_numbers else TEXT.NO_REGISTERED_CARS

    @property
    def car_count(self):
        return len(self._registered_cars)

    @property
    def status(self):
        return TEXT.STATUS[self._registration_status]

    def __del__(self):
        print('invoked')
        if self.car_number in self._registered_cars:
            del self._registered_cars[self.car_number]


if __name__ == '__main__':
    a = Car('AAA-001')
    assert a.car_number == 'AAA-001'
    assert a.registered_cars == 'Registered cars: AAA-001'
    assert a.car_count == 1
    assert a.status == 'Successfully registered'

    b = Car()
    b.car_number = "AAA-002"
    assert b.car_number == 'AAA-002'
    assert b.registered_cars == 'Registered cars: AAA-001, AAA-002'
    assert b.car_count == 2
    assert b.status == 'Successfully registered'

    b.car_number = "AAA-003"
    assert b.car_number == 'AAA-002'
    assert b.registered_cars == 'Registered cars: AAA-001, AAA-002'
    assert b.car_count == 2
    assert b.status == 'The car has already number assigned'

    c = Car('AA1-000')
    assert c.car_number == None
    assert c.registered_cars == 'Registered cars: AAA-001, AAA-002'
    assert c.car_count == 2
    assert c.status == 'Not valid number'

    d = Car()
    d.car_number = 'AAA-002'
    assert d.car_number == None
    assert d.registered_cars == 'Registered cars: AAA-001, AAA-002'
    assert d.car_count == 2
    assert d.status == 'Already registered number'
    del d

    assert c.registered_cars == 'Registered cars: AAA-001, AAA-002'
    assert c.car_count == 2

    del b
    assert len(c._registered_cars) == 1
    assert c.registered_cars == 'Registered cars: AAA-001'
    assert c.car_count == 1

    del a
    assert c.registered_cars == 'There are no registered cars at this moment'
    assert c.car_count == 0

    print('success')