Create subclass from within superclass - Python

Question

I've checked a few of the stackoverflow articles, but couldn't find an answer to my question, so sorry if this is a duplicate. The closes I could find was Instantiate subclass from superclass but this still isn't exactly what I want.

So imagine I have three class: 1 super class and 2 subclasses and I want to do some weird copy method that is the same for all my classes. But in particular, my copy needs to be a new instantiation of said object. Example:

class Pet(object):
    def __init__(self,name):
        self._name = name
    def weird_copy(self):
        name = self._name + " weird"
        z = XXX(name)

class Dog(Pet):
    def __init__(self,name):
        self._name = name + " dog"

class Cat(Pet):
    def __init__(self,name):
        self._name = name + " cat"

The XXX part is where I don't know what to do. If I do

d = Dog('ralph')
d2 = d.weird_copy()

I want d2 to be a Dog object instead of a Pet object. I tried replacing XXX with self and that started causing problems. I know there's a way to do @classmethod, but the problem with that is that I need to use properties from self, so I need to not switch "self" to "cls".

Thanks.

This is a poor design. What if one of the subclasses requires additional arguments to the constructor? — Barmar
– Barmar, Commented Jul 24, 2018 at 20:18
The above is a simplified version of what I actually need. If you have recommendations for a better design, I'm all ears =) — Aram Papazian
– Aram Papazian, Commented Jul 24, 2018 at 21:32
Maybe if you explained what you're really trying to accomplish. Because what you have creates poor dependencies. — Barmar
– Barmar, Commented Jul 24, 2018 at 21:41
In essence it's one object, but it can be represented in different ways. So what I did is made a super that handles most of the functions, but then there are subclasses that will handle particular representations of the super object. So input/output should be the same. Input should be the same for both subobjects but the output will be different. — Aram Papazian
– Aram Papazian, Commented Jul 24, 2018 at 23:34

nosklo · Accepted Answer · 2018-07-24 20:01:23Z

2

type(self) will return a reference to the the class object of the current instance.

def weird_copy(self):
    name = self._name + " weird"
    z = type(self)(name)
    return z

answered Jul 24, 2018 at 20:01

nosklo

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