How to deal with the arguments when inheriting float class in python?

Question

I want to make a new class that is both a float type and has some custom attributes as follows

class Father:
    def __init__(self, a: float, b: str):
        self.a = a
        self.b = b
        print('Father', a, b)


class Son(Father, float):
    def __init__(self, a, b):
        super(Son, self).__init__(a, b)

if __name__ == '__main__':
    son = Son(1, "b")
    print(son.a)

but it reports

TypeError: float expected at most 1 arguments, got 2

I have tried to modified the class Son as follows but it doesn't work.

class Son(Father, float):
    def __init__(self, a, b):
        Father.__init__(a, b)
        float.__init__(self)

Also, the following code reports the same error, but I don't know why.

class Son(float):
    def __init__(self, a, b):
        super(Son, self).__init__(self)

if __name__ == '__main__':
    son = Son(1, "b")
    print(son)

Please update your question with the full error traceback. – quamrana Apr 18 '22 at 08:01 — quamrana, Apr 18 '22 at 08:01

juanpa.arrivillaga · Accepted Answer · 2022-04-18T08:13:34.840

2

So, because you inherit from float you must handle __new__:

class Father:
    def __init__(self, a: float, b: str):
        self.a = a
        self.b = b
        print('Father', a, b)


class Son(Father, float):
    def __new__(cls, a, b):
        # float.__new__ requires a single arugment
        return super().__new__(cls, a)
    def __init__(self, a, b):
        super().__init__(a, b)

if __name__ == '__main__':
    son = Son(1, "b")
    print(son.a)

But you should really consider if instead of inheritance you should be using composition or another approach. Why inherit from float?

edited Apr 18 '22 at 08:13

answered Apr 18 '22 at 08:10

juanpa.arrivillaga

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I think he also can use descriptors instead of inheritance – sudden_appearance Apr 18 '22 at 08:12
And to be noted sum (and most other dunder methods) of 2 sons will produce float `print(type(son + son)) # ` – sudden_appearance Apr 18 '22 at 08:14
@sudden_appearance yes, the built-in types are mostly closed to extension – juanpa.arrivillaga Apr 18 '22 at 08:21
@juanpa.arrivillaga, there are some mixins provided, e.g. `MutableMapping`, but mostly - you're right – sudden_appearance Apr 18 '22 at 08:29

How to deal with the arguments when inheriting float class in python?

1 Answers1