pointer.py

class Pointer(object):
    def __init__(self, target=None):
        self.target = target

    _noarg = object()

    def __call__(self, target=_noarg):
        if target is not self._noarg:
            self.target = target
        return self.target


x = Pointer(2)
y = x
x() # => 2
y() # => 2

y(30)
x() # => 30

x(50)
y() # => y