Metaclass to run a __first__ method for the first instantiation of a class

Question

I had an idea for a __first__ special method for a class. It would be run after __new__ and before __init__ the first time a specific object is instantiated but is not then run if you instantiate the object again. For example, if you run:

class Foo:
    def __first__():
        print('Inside __first__')
    def __init__(self):
        print('Inside __init__')
a = Foo()
b = Foo()

It would return:

Inside __first__
Inside __init__
Inside __init__

In order to try and create this particular syntax I decided to create a meta class so that you could simply add this syntax to a class of your choice. This was my final code for the meta class and it was the first time I have tried meta class syntax so I was interested in what you thought about my code:

class First(type):
    _first = True
    def __call__(cls, *args, **kwargs):
        if cls._first:
            cls._first = False
            cls._oldinit = cls.__init__
            def init(*args, **kwargs):
                cls.__first__()
                cls._oldinit(*args, **kwargs)
            cls.__init__ = init
            cls.__init__.__doc__ = cls._oldinit.__doc__
        else:
            cls.__init__ = cls._oldinit
        return super(First, cls).__call__(*args, **kwargs)