Must I override integer add method to support addition of an integer and object?

Question

So I am making a class called Complex which a representation of imaginary numbers (I know python has its own, but i want to make one myself). Thing is I want to construct an add method that supports addition of complex numbers as well as integers. So:

a = Complex(2, 4) + Complex(1, 1)
b = Complex(0, 3) + 3
c = 2 + Complex(4, 5)

should all be supported. As I understand,

object1 + object2

is the syntactic-sugar-equivalent of

object1.__add__(object2)

First and second examples are fine, but how do I get my class to support addition on the form INTEGER + COMPLEX? Do I have to override integer __add__method, if so; how do I do that, and is there another way?

acushner · Accepted Answer · 2020-12-06 06:36:13Z

4

you have to implement __radd__ on Complex.

the way this works is pretty cool, if there's no existing implementation on an object for __add__, in your case, int + Complex, python will automatically check to see if __radd__ is implemented on the right-hand object.

so it would be like:

- does `int` have `__add__` for `Complex`? no
- does `Complex` have `__radd__` for `int`? yes. cool, we've solved it

the implementation would probably look something like:

class Complex:
    def __radd__(self, other):
        return self + Complex(other)

edited Dec 6, 2020 at 6:36

answered Sep 8, 2019 at 17:27

acushner

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