initializing parent class attributes while making subclass Python

Question

Based on the classes below, I tried to make a dog that would allow instantiating all fields, and I tried:

class Animal(object):
    def __init__(self, legs=4, animal_type='beast'):
        self.legs           = legs
        self.animal_type    = animal_type


class Dog(Animal):
    def __init__(self, name=None, owner=None):
        self.name   = name
        self.owner  = owner

dog = Dog(legs=4, animal_type='dog', name='Fido', owner='Bob')

print dog.owner
print dog.name

which gave TypeError: __init__() got an unexpected keyword argument 'legs'

Based on Initializing subclass variable in Python I tried

class Animal(object):
    def __init__(self, legs=4, animal_type='beast'):
        self.legs           = legs
        self.animal_type    = animal_type


class Dog(Animal):
    def __init__(self, legs=None, animal_type=None, name=None, owner=None):
        if legs:
            self.legs = legs
        if animal_type:
            self.animal_type = animal_type
        self.name   = name
        self.owner  = owner

dog = Dog(name='Fido', owner='Bob')

print dog.name

But here, I got a dog, but legs and animal_type didn't default, in fact, they didn't get set at all (pic below).

This example works to make a dog with 4 legs, but I don't have the ability to default and I have to give the legs and type or it won't create:

class Animal(object):
    def __init__(self, legs=4, animal_type='beast'):
        self.legs           = legs
        self.animal_type    = animal_type


class Dog(Animal):
    def __init__(self, legs, animal_type, name=None, owner=None):
        if legs:
            self.legs = legs
        if animal_type:
            self.animal_type = animal_type
        self.name   = name
        self.owner  = owner

dog = Dog(4, 'dog', name='Fido', owner='Bob')

print dog.name

How can I subclass to be able to optionally overwrite parent attributes that default if they aren't given? So how can I take these classes Animal and Dog, and if I don't say the legs or type get a dog with legs=4, and animal_type=beast? Thank you

deceze · Accepted Answer · 2015-08-17 15:32:35Z

2

class Animal(object):
    def __init__(self, legs=4, animal_type='beast'):
        self.legs        = legs
        self.animal_type = animal_type


class Dog(Animal):
    def __init__(self, name=None, owner=None, **kwargs):
        super(Dog, self).__init__(**kwargs)
        self.name  = name
        self.owner = owner

dog = Dog(legs=4, animal_type='dog', name='Fido', owner='Bob')

Capture the extra arguments in **kwargs and call the parent's constructor with them.

edited Aug 17, 2015 at 15:32

answered Aug 17, 2015 at 14:45

deceze♦

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