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Python Object-Oriented Python Advanced Objects Subclassing Built-ins

Kento Nambara
Kento Nambara
1,764 Points

What is the point of having *args and **kwargs as arguements when overriding __new__ or __init__?

I just cannot understand this concept. I understand init, but I also do not completely understand the concept of new.

Jamaru Rodgers
Jamaru Rodgers
3,046 Points

I would also like a refresher from a fellow student or from the staff! It always gets me. Sorry for bringing up this old post but I saw it didn't have an answer :)

1 Answer

Well I'll say the key usage of dunder init and dunder new are quite similar and different the first handles how an instance of your objects are created at run time with the later contains logic on how the class should be created. The constructor init for instance handles setting instance values while new will often contain a hook to intercept how the class is created detecting if the class has certain attributes and can even contain logic to override the class properties.

For example

class A(object):
    def __init__(self, count=0):
        self.count = count


class A(object):  # -> don't forget the object specified as base

    def __new__(cls):
        print("A.__new__ called")
        return super(A, cls).__new__(cls)

    def __init__(self):
        print("A.__init__ called")


# A()
# A.__new__ called
# A.__init__ called

Check out https://spyhce.com/blog/understanding-new-and-init and https://howto.lintel.in/python-__new__-magic-method-explained/ for more information.