CODEWITHSUNDEEP
pythoninheritanceoverriding
davekr
davekr

Reputation: 2276

inheritance on class attributes (python)

Is there a way to accomplish something like this? I work in Python, but I am not sure if there is a way to do it in any programming language...

class Parent():
    class_attribute = "parent"

    @staticmethod
    def class_method():
        print __class__.class_attribute

class Child(Parent):
    class_attribute = "child"

I know I can't call __class__ directly. Its just an example, because I would want something like reference to the class itself, because I want the child class to act differently based on its class_attribute.

And then supposed output should be like this:

> Parent.class_method()
"parent"
> Child.class_method()
"child"

I know the same technique can be accomplish through the instances. But I don't want to create instances, because sometimes the code within the __init__ method could be long and demanding and if I would want to call class_method often, I would have to create plenty of instances used just for this one method call. And because class_attribute and class_method are static and won't be changed by instances.

Upvotes: 7

Views: 4491

Answers (2)

Daniel Roseman
Daniel Roseman

Reputation: 599450

Er, sounds like you want a classmethod, which not surprisingly is done with the classmethod decorator:

class Parent(object):
    class_attribute = "parent"

    @classmethod
    def class_method(cls):
        print cls.class_attribute

class Child(Parent):
    class_attribute = "child"


>>> Parent.class_method()
parent
>>> Child.class_method()
child

Or, as bgporter points out, you can do it directly with the attributes, with no need for the methods at all.

Upvotes: 10

bgporter
bgporter

Reputation: 36454

It just works in Python, with or without creating instances:

>>> class Parent(object):
...    attribute = "parent"
... 
>>> class Child(Parent):
...    attribute = "child"
... 
>>> p = Parent()
>>> p.attribute
'parent'
>>> c = Child()
>>> c.attribute
'child'
>>> Parent.attribute
'parent'
>>> Child.attribute
'child'
>>>

Upvotes: 4

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