class Chain:
    def __init__(self, *tasks):
        self._tasks = tasks
    
    def __rshift__(next_task):
        self._tasks[-1] >> next_task
        
    def __lshift__(prev_task):
        self._tasks[0] << prev_task


def foo():
    two = DummyOperator(task_id="two")
    three = DummyOperator(task_id="three")
    return Chain(two, three)


one = DummyOperator(task_id="one")
four = DummyOperator(task_id="four")
one >> foo() >> four

class Chain:
    def __init__(self, *tasks):
        self._tasks = tasks
    
    def __rshift__(next_task):
        self._tasks[-1] >> next_task
        
    def __lshift__(prev_task):
        self._tasks[0] << prev_task


def foo():
    two = DummyOperator(task_id="two")
    three = DummyOperator(task_id="three")
    return Chain(two, three)


one = DummyOperator(task_id="one")
four = DummyOperator(task_id="four")
one >> foo() >> four