squared functions--most Pythonic way?

[Luigi Ballabio]

Hi all,
      suppose we want to define a function which, given f(x), returns 
its square. There are a number of ways which come to mind, such as:

object-oriented programming:

    def fsquare:
        def __init__(self,f):
            self.f = f
        def __call__(self,x):
            return self.f(x)**2

functional programming:

    # with an internal named function
    def fsquare(f):
        def f2(x):
            return f(x)**2
        return f2

    # with lambda
    def fsquare(f):
        return lambda x: f(x)**2

and I'm sure people can come out with others that I didn't figure but 
are obvious to any Dutchmen.

My question: is any of the above considered more Pythonic? 

Thanks,
         Luigi