class A:

......

class B(A):

.......


aA = A()

a = A()
a.__class__ = B

a = A()
b = B()
b.__dict__ = a.__dict__.copy()
del a
a = b
del b

>>> from collections import Counter
>>> d = dict(a=1, b=0)
>>> +Counter(d)
Counter({'a': 1})

class A:
    def back_print(a: str) -> None:
        print(a[::-1])

class B(A):
    def foo(self,a,b):
        print(a+b)

b = B()
print(type(b))

# строим функцию, которая будет добавлена как метод "а-ля" класс B()

def foo(self,a,b):
    print(a, '+', b)

aA = A()
aA.foo = foo.__get__(aA)
aA.foo(2,3)
print(type(aA))

# подменяем тип:
aA.__class__ = type(b)
if type(aA)==type(b):
    print(' type(aA)==type(b) ')

def bind(instance, method):
    def binding_scope_fn(*args, **kwargs):
        return method(instance, *args, **kwargs)
    return binding_scope_fn

bA = A()
bA.foo = bind(bA, foo)

aA.foo(2,3)
print(type(bA))

import types
cA = A()
cA.foo = types.MethodType(foo, cA)
cA.foo(2,3)
print(type(cA))

cA.__class__ = type(b)
cA.foo(2,3)
b.foo(2,3)
if type(cA)==type(b):
    print(' type(cA)==type(b) ')

cA.pro = 7
print(f'cA.pro: {cA.pro}')

cA.pro: 7