how to use super().__add__ in a derived class

user_429400 0
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My code works but I'm not sure if this the correct way to implement it. I'm trying to use the base class "add" method in the derived class. super().__add__ returns a base class therefore I must somehow "convert" the class back to the derived type before returning it. Can you please take a look and tell me if there is a better/ nicer way to implement this?

class a:
def __init__(self, x, y):
    self.x = x
    self.y = y

def __repr__(self):
    return f"{self.x} {self.y}"

def __add__(self, other):
    return a(self.x + other.x, self.y + other.y)



class b(a):
    def __init__(self, x, y, z):
        super().__init__(x, y)
        self.z = z

    def __repr__(self):
        str = super().__repr__()
        return str + f" {self.z}"

    def __add__(self, other):
        temp = super().__add__(other)
        new_z = self.z + other.z
        return b(temp.x, temp.y, new_z)

Thanks! LI

operator-overloading inheritance python
1 Answers

You can make the constructor of class b compatible with that of the base class by making the additional parameter z optional with a default value:

class b(a):
    def __init__(self, x, y, z=0):
        super().__init__(x, y)
        self.z = z

so that the __add__ method of the base class can instantiate a new object by the type of the self object rather than a hard-coded class:

class a:
    def __add__(self, other):
        return type(self)(self.x + other.x, self.y + other.y)

and that the __add__ method of the derived class can modify the object returned by the __add__ method of the base class directly before returning it:

def __add__(self, other):
    temp = super().__add__(other)
    temp.z = self.z + other.z
    return temp

Demo: https://replit.com/@blhsing/UnusedDraftyPortablesoftware

user_68909120
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