# How to overload \_\_add\_\_ method in a self made class to sum multiple objects of the class? **URL:** \ **Category:** Python Help\ **Created:** [December 7, 2023, 1:20pm UTC](https://discuss.python.org/t/how-to-overload-add-method-in-a-self-made-class-to-sum-multiple-objects-of-the-class/40543 "2023-12-07T13:20:17Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![dragonsoul](https://avatars.discourse-cdn.com/v4/letter/d/c0e974/32.png) [@dragonsoul](https://discuss.python.org/u/dragonsoul)\ **Post date:** [December 7, 2023, 1:20pm UTC](https://discuss.python.org/t/how-to-overload-add-method-in-a-self-made-class-to-sum-multiple-objects-of-the-class/40543/1 "2023-12-07T13:20:17Z")
```python class MyClass: def __init__ (self, value): self.value = value def __add__ (self, other): if isinstance(other, MyClass): return self.value + other.value elif isinstance(other, int) or isinstance(other, float): return self.value + other else: raise TypeError("Unsupported operand type(s) for +") # Creating objects of MyClass obj1 = MyClass(10) obj2 = MyClass(20) obj3 = MyClass(30) # Adding multiple objects using the + operator result = obj1 + obj2 + obj3 print(result) # Output: 60 ``` I have received this solution from chat gpt but this does not work. I can’t sum more than 2 objects of my class. How can i solve this?;D (sorry for bad English) ---
**Author:** ![ajoino](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/ajoino/32/6907_2.png) [@ajoino](https://discuss.python.org/u/ajoino)\ **Post date:** [December 7, 2023, 1:37pm UTC](https://discuss.python.org/t/how-to-overload-add-method-in-a-self-made-class-to-sum-multiple-objects-of-the-class/40543/2 "2023-12-07T13:37:50Z")
Your ` __add__ ` currently returns an object of whatever type `MyClass.value` is. To be able to chain additions, the ` __add__ ` method should return a `MyClass` instance. ---
**Author:** ![ajoino](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/ajoino/32/6907_2.png) [@ajoino](https://discuss.python.org/u/ajoino)\ **Post date:** [December 7, 2023, 1:39pm UTC](https://discuss.python.org/t/how-to-overload-add-method-in-a-self-made-class-to-sum-multiple-objects-of-the-class/40543/3 "2023-12-07T13:39:14Z")
Or you might be able to add an ` __radd__ ` method, but not 100% sure about that. ---
**Author:** ![WeisLeDocto](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/weisledocto/32/15827_2.png) [@WeisLeDocto](https://discuss.python.org/u/WeisLeDocto)\ **Post date:** [December 7, 2023, 2:15pm UTC](https://discuss.python.org/t/how-to-overload-add-method-in-a-self-made-class-to-sum-multiple-objects-of-the-class/40543/4 "2023-12-07T14:15:56Z")
Hi ! When adding two objects in Python, the order of the two objects around the `+` operator matters ! When you call `obj1 + obj2 + obj3`, `obj1 + obj2` is first evaluated and returns an integer (30). Then, `30 + obj3` is evaluated, but the type of 30 (`int`) does not implement addition with objects of type `MyClass`, and you get an error. If you now call `obj1 + (obj2 + obj3)`, `(obj2 + obj3)` is first evaluated and returns an `int` (50). Then, `obj1 + 50` is evaluated, and since the ` __add__ ` method of `MyClass` supports addition with objects of type `int`, you get the expected result 60 (try it !). As @ajoino mentioned, the ` __radd__ ` method can solve your problem. Basically, in case the addition first fails (like in `30 + obj3`), it will try the same operation with reversed operands (`obj3 + 30`). The following code works for me: ```auto class Myclass: def __init__ (self, value): self.value = value def __add__ (self, other): if isinstance(other, Myclass): return self.value + other.value elif isinstance(other, int) or isinstance(other, float): return self.value + other else: raise TypeError("Unsupported operand type(s) for +") def __radd__ (self, other): return self. __add__ (other) if __name__ == " __main__": obj1 = Myclass(10) obj2 = Myclass(20) obj3 = Myclass(30) result = obj1 + obj2 + obj3 print(result) ``` ---
**Author:** ![hansgeunsmeyer](https://sea2.discourse-cdn.com/flex002/user_avatar/discuss.python.org/hansgeunsmeyer/32/15188_2.png) [@hansgeunsmeyer](https://discuss.python.org/u/hansgeunsmeyer)\ **Post date:** [December 7, 2023, 2:45pm UTC](https://discuss.python.org/t/how-to-overload-add-method-in-a-self-made-class-to-sum-multiple-objects-of-the-class/40543/5 "2023-12-07T14:45:38Z")
As Antoine wrote - you should add an ` __radd__ ` method in order to be able to add numerical values to objects of MyClass. But as @ajoino wrote, you should also let your ` __add__ ` method return objects of MyClass; your initial problem was caused by not doing so. It’s formally possible to have the ` __add__ ` method return other types, but it will create a lot of confusion in using the addition operator (as you already noticed yourself). So, you could change the method to this (or sth similar): ```auto def __add__ (self, other): if isinstance(other, MyClass): return MyClass(self.value + other.value) elif isinstance(other, int) or isinstance(other, float): return MyClass(self.value + other) else: raise TypeError("Unsupported operand type(s) for +") ``` If you implement those methods, it’s usually also good to implement ` __iadd__ ` in order to support `+=`. For a more elaborate example, see: [numbers — Numeric abstract base classes — Python 3.12.0 documentation](https://docs.python.org/3/library/numbers.html#implementing-the-arithmetic-operations). ---
**Author:** ![dragonsoul](https://avatars.discourse-cdn.com/v4/letter/d/c0e974/32.png) [@dragonsoul](https://discuss.python.org/u/dragonsoul)\ **Post date:** [December 9, 2023, 7:46pm UTC](https://discuss.python.org/t/how-to-overload-add-method-in-a-self-made-class-to-sum-multiple-objects-of-the-class/40543/6 "2023-12-09T19:46:23Z")
Wow that’s great. I was just looking for such this answer:D. Thank you so much man.🙂