The code presented in the editor shows how to use the class method as an alternative constructor, allowing you to handle an additional argument.
The including_brand method is a class method, and expects a call with two parameters ('vin' and 'brand'). The first parameter is used to create an object using the standard __init__ method.
In accordance with the convention, the creation of a class object (i.e., calling the __init__ method, among other things) is done using cls(vin).
Then the class method performs an additional task – in this case, it supplements the brand instance variable and finally returns the newly created object.
The result of the presented code:
Ordinary __init__ was called for ABCD1234
Class method was called
Ordinary __init__ was called for DEF567
ABCD1234
DEF567 NewBrand
output
As you can see, for the car with vin=ABCD1234, the __init__ method has been called by default.
For the car with vin=DEF567, the class method has been called, which calls the __init__ method and then performs additional actions and returns the object.
Code
class Car:def __init__(self, vin):
print('Ordinary __init__ was called for', vin)
self.vin = vin
self.brand = ''
@classmethod
def including_brand(cls, vin, brand):
print('Class method was called')
_car = cls(vin)
_car.brand = brand
return _car
car1 = Car('ABCD1234')
car2 = Car.including_brand('DEF567', 'NewBrand')
print(car1.vin, car1.brand)
print(car2.vin, car2.brand)