class Synchronizer:
def __init__(self):
self.due_calls = ListModel(deque())
self.done_calls = ListModel(deque())
def add_call(self, call):
self.due_calls.append(call)
def perform_one_call(self):
self.due_calls[0]()
self.done_calls.append(self.due_calls.pop(0))
def __init__(self):
self.due_calls = ListModel(deque())
self.done_calls = ListModel(deque())
