Python Forum

class Sample:

    def __new__(cls, *args, **kwargs):
        print("__new__(), Has been called")
        print('cls: ', cls)
        print('args: ', args)
        print('kwargs: ', kwargs)

        # create new object
        obj = super().__new__(cls, *args, **kwargs)

        # return object
        return obj

    def __init__(self, x=0, y=0):
        print("__init__(), Has been called")
        print('self: ', self)
        self.x = x
        self.y = y

sample_1 = Sample()

Output:
__new__(), Has been called
cls:  <class '__main__.Sample'>
args:  ()
kwargs:  {}
__init__(), Has been called
self:  <__main__.Sample object at 0x000002425DED2450>

sample_2 = Sample(3, 6)

Output:
__new__(), Has been called
cls:  <class '__main__.Sample'>
args:  (3, 6)
kwargs:  {}

Error:
Traceback (most recent call last):
  File "<pyshell#50>", line 1, in <module>
    sample_2 = Sample(3, 6)
  File "<pyshell#46>", line 10, in __new__
    obj = super().__new__(cls, *args, **kwargs)
TypeError: object.__new__() takes exactly one argument (the type to instantiate)

sample_3 = Sample(x=3, y=6)

Output:
__new__(), Has been called
cls:  <class '__main__.Sample'>
args:  ()
kwargs:  {'x': 3, 'y': 6}

Error:
Traceback (most recent call last):
  File "<pyshell#51>", line 1, in <module>
    sample_3 = Sample(x=3, y=6)
  File "<pyshell#46>", line 10, in __new__
    obj = super().__new__(cls, *args, **kwargs)
TypeError: object.__new__() takes exactly one argument (the type to instantiate)

obj = super().__new__(cls, *args, **kwargs)

obj = super().__new__(cls)

obj = super().__new__(cls)

https://docs.python.org/3/reference/data...ct.__new__ Wrote:object.__new__(cls[, ...])
Called to create a new instance of class cls. __new__() is a static method (special-cased so you need not declare it as such) that takes the class of which an instance was requested as its first argument. The remaining arguments are those passed to the object constructor expression (the call to the class). The return value of __new__() should be the new object instance (usually an instance of cls).

Typical implementations create a new instance of the class by invoking the superclass’s __new__() method using super().__new__(cls[, ...]) with appropriate arguments and then modifying the newly created instance as necessary before returning it.

If __new__() is invoked during object construction and it returns an instance of cls, then the new instance’s __init__() method will be invoked like __init__(self[, ...]), where self is the new instance and the remaining arguments are the same as were passed to the object constructor.

If __new__() does not return an instance of cls, then the new instance’s __init__() method will not be invoked.

__new__() is intended mainly to allow subclasses of immutable types (like int, str, or tuple) to customize instance creation. It is also commonly overridden in custom metaclasses in order to customize class creation.