class Base:
    def open(self): pass
    def read(self): pass
 
class A(Base):
    def read(self): pass
 
class B(Base):
    def read(self): pass
 
class Mixin:
    def feature(self): pass
 
class Proxy(Base):
    def __init__(self, item, mixin):
        self.__item = item
        self.__mixin = mixin
 
    def __getattr__(self, name):
        try:
            return getattr(self.__item, name)
        except AttributeError:
            return getattr(self.__mixin, name).__get__(name)
 
for Item in (A, B):
    item = Item()
    item = Proxy(item, Mixin)
    assert isinstance(item, Base)
    assert item.open.__func__ is Base.open
    assert item.read.__func__ is Item.read
    assert item.feature.__func__ is Mixin.feature
    assert item.__Proxy_item is item
    assert item.__Proxy_mixin is Mixin

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