import types
 
class customizable:
    def __init__(self, method):
        self.method = method
 
    def __set_name__(self, owner, name):
        self.name = name
 
    def __get__(self, obj, obj_type=None):
        if obj:
            try:
                return vars(obj)[self.name]
            except KeyError:
                return self.method.__get__(obj, obj_type)
        return self.method
 
class Foo():
    @customizable
    def __getitem__(self, x):
        return x
 
def new_get(self, x):
    return x + 1
 
x = Foo()
y = Foo()
x.__getitem__ = types.MethodType(new_get, x)
print(Foo.__getitem__)
print(x[42])
print(y[42])

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