future.py

class Future(object):
    def __call__(self, *args, **kwargs):
        return self._perform(lambda: self._value(*args, **kwargs))
    def __getattr__(self, name):
        if name[0] == "_":
            return self.__dict__[name]
        return self._perform(lambda: getattr(self._value, name))
    def __setattr__(self, name, value):
        if name[0] == "_":
            self.__dict__[name] = value
            return
        self._perform(lambda: setattr(self._value, name, value))
    def reify(self):
        self._reify()
        return self._value

class Timeline(object):
    def __init__(self):
        self._actions = []
    def _fulfill_future(self, weak_future, func):
        result = func()
        future = weak_future()
        if future is not None:
            future._value = result
    def _create_future(self):
        future = Future()
        future._perform = self.perform
        future._reify   = self.reify
        return future
    def perform(self, action):
        import functools, weakref
        future = self._create_future()
        weak_future = weakref.ref(future)
        action = functools.partial(self._fulfill_future, weak_future, action)
        self._actions.append(action)
        return future
    def map(self, func):
        return lambda *args, **kwargs: self.perform(
            lambda: func(*(x._value for x in args),
                         **dict((k, v._value) for k, v in kwargs.items()))
        )
    def pure(self, func):
        return lambda *args, **kwargs: self.perform(
            lambda: func(*args, **kwargs)
        )
    def reify(self):
        for action in self._actions:
            action()
        self._actions.clear()

# ----------------------------------------------------------------------------
# Example
# ----------------------------------------------------------------------------

class Foo(object):
    pass

t = Timeline()

t.pure(print)("hi")
inp = t.pure(input)("enter a string!")
inp = inp.upper()
foo = t.pure(Foo)()
foo.sdlkf = "ok."
t.map(lambda inp: print("here's your string in uppercase: " + inp))(inp)
t.map(print)(foo.sdlkf)

print("let's begin!")
t.reify()