Well.

gistfile1.py

def decorated(func):

    def r_func(*args, **kwargs):
        print "Decorated call."
        return func(*args, **kwargs)

    return r_func

@decorated
def double(x):
    return 2 * x

if __name__ == "__main__":

    print(double(2)) # -> Decorated call.
                     # -> 4

    double_undec = double.func_closure[0].cell_contents
    print(double_undec(2)) # -> 4