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mauricio
Asked: 2020-03-24 15:56:33 +0800 CST 2020-03-24 15:56:33 +0800 CST

Why can't I use multiple inheritance?

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I am learning Python I hope they are flexible. I want to check whether multiple inheritance worked or not, so I want this class to dog:

class dog(animal,to_jump):
    def __init__(self,name):
        self.name = name
    print(f"my dog {self.name} is barking and he is {self.var}")

also inherit the method from this:

class to_jump:
    #this is a method
    def jump(self):
        self.var = "jumping"

to check it I want to print what is in the class variable to_jump (self.var) but in another class, I want it to do this printing correctly.

print(f"my dog {self.name} is barking and he is {self.var}")

and it throws me this error.

File "herencia.py", line 18, in __init__
    print(f"my dog {self.name} is barking and he is {self.var}"
AttributeError: 'dog' object has no attribute 'var'

this is the instance of the dog class.

instancia = dog("bruno")
python

1 Answers

  1. Best Answer

    It's not a problem of inheritance, it's a problem of where you create the instance attribute. self.varis created in jump, it does not exist before it jumpis called , neither in the parent class nor in Dog.

    >>> inst = to_jump()
>>> inst.var
Traceback (most recent call last):

  File "main", line 1, in <module>
    inst.var

AttributeError: 'to_jump' object has no attribute 'var'

>>> inst.jump()
>>> inst.var
'jumping'

    If you call the inherited method in the initializer jumpbefore trying to use the instance attribute, there is no problem:

    class Animal:
    pass

class Saltarin:
    def jump(self):
        self.var = "jumping"

class Dog(Animal, Saltarin):
    def __init__(self,name):
        self.name = name
        self.jump()
        print(f"my dog {self.name} is barking and he is {self.var}")


instancia = Dog("bruno")

    This is one of the reasons why it's always good practice to initialize all instance attributes in the class initializer:

    class Animal:
    def __init__(self):
        self.vive = True
        super().__init__()

class Saltarin:
    def __init__(self):
        self.estado = "corriendo"
        super().__init__()

    def saltar(self):
        self.estado = "saltando"

class Perro(Animal, Saltarin):
    def __init__(self, nombre):
        super().__init__()
        self.nombre = nombre
        print(f"Mi pero {self.nombre} está ladrando y está {self.estado}")
        self.saltar()
        print(f"Mi pero {self.nombre} está ladrando y está {self.estado}")


instancia = Perro("Bruno")

    Mi pero Bruno está ladrando y está corriendo
Mi pero Bruno está ladrando y está saltando
    • 2