CODEWITHSUNDEEP
pythonreturninstantiation
Snusifer
Snusifer

Reputation: 553

Return different type upon class instantiation?

So I am making my own version of a Complex class which works as a representation of imaginary numbers: Complex(a, b) where a + bi.

Thing is, I want to return something else based on arguments given. Im pretty sure I have to use the magic method new but I cant seem to be able to handle the arguments given. For instance:

a = Complex(4, 5)
print(a)
> Complex(4, 5)
b = Complex(3, 0)
print(b)
> 3
c = Complex(0, 0)
print(c)
> 0

I want the b and c variables to be assigned numerical values. Not some sort of to-string solution where the class pretends to be something it is not. How can I do this?

Thanks for replies :))

Upvotes: 0

Views: 79

Answers (3)

new Q Open Wid
new Q Open Wid

Reputation: 2303

As said, new is a lot easier than other solutions because everything is fit up together. You could just say that if the second arg is zero then return a else call __new__ again.

I this this might be exactly what you need because you pointed out that you struggled with finding a solution.

Upvotes: 0

Zecong Hu
Zecong Hu

Reputation: 3224

As others have pointed out in comments, this is exactly what __new__ is for.

Here's what happens when you create an instance of a class Complex:

  1. You write Complex(a, b).
  2. Complex.__new__(a, b) is called, and by default (that is, if you don't override the __new__ method) this returns an empty object of type Complex.
  3. If the object returned by Complex.__new__(a, b) (let's denote it as cmplx) is actually of type Complex, call cmplx.__init__(a, b), or equivalently, Complex.__init__(cmplx, a, b).

For your case, simply return an int in the __new__ method when the second argument is called, and call the __new__ method of the super class otherwise. That is:

class Complex:
    def __new__(cls, a, b):
        if b == 0:
            return a
        return super().__new__(cls)  # or equiv.: object.__new__(cls)

Upvotes: 3

Paul M.
Paul M.

Reputation: 10809

Not some sort of to-string solution where the class pretends to be something it is not.

Isn't this exactly what you'd use __str__ for, though? Maybe I'm not understanding you correctly, but if you're worried you wont be able to do math with your objects, you would just implement the relevant magic methods, such as __add__.

Upvotes: 0

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