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class State_d:
    def __init__(self, imp):
        self.__implementation = imp
    def changeImp(self, newImp):
        self.__implementation = newImp
    # Delegate calls to the implementation:
    def __getattr__(self, name):
        return getattr(self.__implementation, name)

class Implementation1:
    def f(self):
        print("Fiddle de dum, Fiddle de dee,")
    def g(self):
        print("Eric the half a bee.")
    def h(self):
        print("Ho ho ho, tee hee hee,")

class Implementation2:
    foo =1 
    def f(self):
        print("We're Knights of the Round Table.")
    def g(self):
        print("We dance whene'er we're able.")
    def h(self):
        print("We do routines and chorus scenes")


    

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def run(b):
    b.f()
    b.g()
    b.h()
    b.g()

b = State_d(Implementation1())
run(b)


    

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b.changeImp(Implementation2())
run(b)


    

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b.foo = 100


    

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b.foo


    

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b = State_d(Implementation1())
run(b)


    

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try:
    b.foo
except:
    print("no implementation")


    

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