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Python: is there a use case for modifying an instance class?

Related: Convert Python Objects

I recently found out that Python allows you to change the instance class as follows:

class Robe:
    pass

class Dress:
    pass

r = Robe()
r.__class__ = Dress

I am trying to find out if there is a case where the "transmutation" of such an object can be useful. I came across this in IDLE, and one thing I noticed is that assigning another class does not call the new class method __init__, although this can be done explicitly if necessary.

Almost every use case that I can think of will be better served by the composition, but I am encoding newb, so I know.;)

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2 answers

, Robe Dress. , , , .

, factory . :

class Base(object):
    pass

def base_factory():
    return Base()  # in real code, this would probably be something opaque

def Derived(Base):
    def __new__(cls):
        self = base_factory()     # get an instance of Base
        self.__class__ = Derived  # and turn it into an instance of Derived
        return self

Derived class __new__ base_factory, Base. factory - , , ( Base() super(Derived, cls).__new__(cls) , ).

instance __class__ , Derived.__new__ Derived, , Derived.__init__ ( ).

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