python: substituting class

1.py

class A:
    qux = 'A'
    def __init__(self, name):
        self.name = name
    def foo(self):
        print('foo')

class B:
    qux = 'B'
    def bar(self):
        print('bar')

a = A('a')

print(a.__class__)   # <class '__main__.A'>
print(a.__dict__)    # {'name': 'a'}
print(a.qux)         # A
a.foo()              # foo

a.__class__ = B

print(a.__class__)   # <class '__main__.B'>
print(a.__dict__)    # {'name': 'a'}
print(a.qux)         # B
# a.foo()            # AttributeError: 'B' object has no attribute 'foo'
a.bar()              # bar