Python inheritance: How can I update a parent attribute when creating a child's subclass?

Question

Trying to understand multiple inheritance.

I have created a parent class called 'Human' and from it created a child class called 'Man'. This child class inherits all attributes and methods except that the human_gender attribute is overwritten and set to 'male'. - this all works fine and as expected.

What I then tried to do it created a new child class called 'BoyChild' (from 'Man') which I hoped would inherit all of man's attributes and methods except that I wished to overwrite the age attribute to set the age to 8. This is throwing up an error.

Why is this error occurring? If I remove 'age=8' from the super().init parentheses, it inherits as normal, but I can't seem to overwrite the inherited class' attribute 'age'.

class human():
    '''This is a human class'''
    def __init__(self, human_gender = "unknown", age = 0,
                    hunger_level=0):
        self.human_gender = human_gender
        self.age = age
        self.hunger_level = hunger_level

    def setGender(self):
        self.human_gender = input("Please enter human's gender:")

    def setAge(self):
        self.age = int(input("Please enter human's age"))

    def setHunger_level(self):
        self.hunger_level = int(input("Please enter human's hunger level (0-10)"))

class man(human):
    '''This is a Man class'''
    def __init__(self):
        super().__init__(human_gender="male")

class boychild(man):
    '''This is a Boychild class'''
    def __init__(self):
        super().__init__(age=8)


guy = boychild()
#guy.setGender()
#guy.setAge()
guy.setHunger_level()
print("The human is a: ", guy.human_gender)
print("The human is: ", guy.age)
print("The human's hunger level is: ", guy.hunger_level)

input()

tynn · Accepted Answer · 2015-06-15 07:45:34Z

4

The __init__ method of man doesn't accept keyword arguments at all. But since you rely on it to work, you should use them:

class man(human):
    '''This is a Man class'''
    def __init__(self, **kwargs):
        super().__init__(human_gender="male", **kwargs)

class boychild(man):
    '''This is a Boychild class'''
    def __init__(self, **kwargs):
        super().__init__(age=8, **kwargs)

This way you catch every argument not handled by your class and just passt it on.

answered Jun 15, 2015 at 7:45

tynn

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1 Comment

sw123456 Over a year ago

Brilliant! Very clear and helpful. Exactly what I needed. Thank you!

Mel · Accepted Answer · 2015-06-15 07:44:45Z

3

The class boychild inherits the class man. Therefore, when you call super().__init__(age=8), it refers to man.__init__, that have no arguments.

You could do something like this:

class man(human):
    '''This is a Man class'''
    def __init__(self, age = 0, hunger_level=0):
        super().__init__(human_gender="male", age, hunger_level)

answered Jun 15, 2015 at 7:44

Mel

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