Inheritance from parent class return attribute error-CodePudding

Hi I tried to inheritance some code from a class :

class MathParent:
    def multiply(self, number1, number2):
        self.answer = number1 * number2
        return self.answer
    def happy(self):
        return "Nice Mark!"

class MathChild(MathParent):
    def plus_x(self, x) :
        return self.answer   x

p_out = MathParent()
print(p_out.multiply(5, 2))
print(p_out.happy())

c_out = MathChild()
print(c_out.happy())
print(c_out.plus_x(5))

that happy methods has successfully inherited, but when I access self.answer attribute, it raise error. I use another way :

return MathParent.self.answer   x

And that still didn't work. Any insight will be very helpful :)

CodePudding user response：

self.answer is only declared whenever multiply is called. You can add constructors as harshraj22 states, but within the existing code, you need to call multiply before calling plus_x.

This:

c_out = MathChild()
print(c_out.happy())
c_out.multiply(1, 1)
print(c_out.plus_x(5))

runs without errors.

CodePudding user response：

self.answer variable is created only when multiply function is run. One way to fix this is, you can use the following to make sure the variable is created once the __init__ is called:


class MathParent:
    def __init__(self) -> None:
        self.answer = 0

    def multiply(self, number1, number2):
        self.answer = number1 * number2
        return self.answer
    def happy(self):
        return "Nice Mark!"

class MathChild(MathParent):
    def plus_x(self, x) :
        return self.answer   x

p_out = MathParent()
print(p_out.multiply(5, 2))
print(p_out.happy())

c_out = MathChild()
print(c_out.happy())
print(c_out.plus_x(5))