例如：
class Queue:
def __init__(self, contents):
self._hiddenlist = list(contents)
def push(self, value):
self._hiddenlist.insert(0, value)
def pop(self):
return self._hiddenlist.pop(-1)
def __repr__(self):
return "Queue({})".format(self._hiddenlist)
queue = Queue([1, 2, 3])
print(queue)
queue.push(0)
print(queue)
queue.pop()
print(queue)
print(queue._hiddenlist)
结果：
>>> Queue([1, 2, 3]) Queue([0, 1, 2, 3]) Queue([0, 1, 2]) [0, 1, 2] >>>