为什么删除双端队列失败的元素？

Question

我运行代码如下：

q = deque([4,5,6,7,8])
for e in q:
    print("remove the {0}".format(e))
    q.remove(e)

Traceback (most recent call last):
  File "C:\Program Files\Python365\lib\site-packages\IPython\core\interactiveshell.py", line 2963, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-18-63a1d575cfeb>", line 1, in <module>
    for e in q:
RuntimeError: deque mutated during iteration
remove the 4

为什么会引发 RuntimeError？

Answer 1

您不能在迭代时编辑双端队列。如果你想一个一个地删除它的元素，你必须迭代它的一个副本：

q = deque([4,5,6,7,8])
copy = list(q)

for e in copy:
    print("remove the {0}".format(e))
    q.remove(e)

或者，如果您想一次删除所有元素：

q.clear()

Answer 2

您无法在迭代时修改 deque。

队列的典型模式是使用 while 循环，并从所需的一端删除项目，使用 deque.pop() 或 deque.popleft()。

例如：

>>> q = deque([4,5,6,7,8])
>>> while q:
...     element = q.pop()
...     print('removed {}'.format(element))
...
removed 8
removed 7
removed 6
removed 5
removed 4

或：

>>> q = deque([4,5,6,7,8])
>>> while q:
...     element = q.popleft()
...     print('removed {}'.format(element))
...
removed 4
removed 5
removed 6
removed 7
removed 8

为什么删除双端队列失败的元素？

why remove element of deque Fail?

python

deque