Python magic method __class__

Question

class C1:
a=4

class C2:
a = 5

c = C1()
c.__class__ = C2
print(c.a)

Above code is one of the quizzes in the challenge.
The answer is 5, which means instance c got 5 from class C2.

I wanted to know how the instance can call the method __class__ if it’s not written in class C2. I remember from other codes that magic method __init__ was written in class to be called. Why the method __class__ wouldn’t need to be written up?

Answer 1

Every object has __class__ attribute(may be few exceptions) ,which contains the class from which the object is created(or instantiated) and the code modifies the __class__ attribute value to other class and hence this object now will be the instance of the changed class

ADDITIONAL INFORMATION(USEFUL):
https://www.honeybadger.io/blog/JUMP_LINK__&&__python__&&__JUMP_LINK-instantiation-metaclass/

Answer 2

c = None

(class C1: ... ; c = C1()) == (class C1: ... ; c.__class__ = C1)

they mean the same thing. everything in python is an object, meaning it has a class. everything in python has that ".__class__" attribute and it deals with the lower levels of python, noted by the double underscore. Everything is part of a base class, and that base class has all these main methods, including __class__ and __init__. Everything made from this class, (everything in pthon) inherits these attributes. Look into classes and subclasses for more info!

Answer 3

My two cents on this topic. The shown example gives that output, because "a" is a class variable, not an instance variable. Consider this:
>>> class C1:
... a=1
... def __init__(self):
... self.b=11
...
>>> class C2:
... a=2
... def __init__(self):
... self.b=22
...
>>> c = C1()
>>> print(c.a, c.b)
1 11
>>> c.__class__ = C2
>>> print(c.a, c.b)
2 11
>>>