Python 3.7.7 文档
collections - Container datatypes
deque读作“deck”（“double-ended queue”)
- Returns a newdequeobject initialized left-to-right (using append()) withdata from iterable. If iterarble is not specified, the newdeque is empty.
- Deques support thread-safe, memory efficient appends and pops from either side of the deque with approximately the same O(1) performance in either direction.
| Method | 作用 |
|---|---|
| maxlen | deque的最大长度，maxlen值为None则没有大小限制 |
| append(x) | 在deque右端加入元素x |
| appendleft(x) | 在deque左端加入元素x |
| clear() | 清空队列，deque长度变为0 |
| copy() | Create a shallow copy of the deque |
| count(x) | 计算deque中等于x的元素的数量 |
| extend(iterable) | 在右端逐个添加iterable参数中的元素 |
| extendleft(iterable) | 在左端逐个添加iterable参数中的元素 ；添加部分的显示顺序和extend中相反 |
| index(x[, start[, stop]]) | 与list的index方法相似 or 返回ValueError |
| insert(i, x) | 与list的insert方法相似 or 插入元素使得长度超过maxlen时， 返回IndexError |
| pop() | 删除并返回最右端元素 or 无元素时，返回IndexError |
| popleft() | 删除并返回最左端元素 or 无元素时，返回IndexError |
| remove(x) | 删除第一个出现的x值，没有的话返回ValueError |
| reverse() | Reverse the elements of the deque in-place and then return None |
| rotate(n=1) | n值为正，向右转动；n值为负，向左转动；rotate(n=-1)等价于d.appendleft(d.pop()), rotate(n=-1)等价于d.append(d.popleft()) |
- Deques support iteration, pickling, len(d), reversed(d), copy.copy(d), copy.deepcopy(d), membership testing with the in operator, and subscript references such as d[-1].
- Indexed access is O(1) at both ends but slows to O(n) in the middle. For fast random access, use lists instead.
>>> from collections import deque
# 创建 deque
>>> d = deque()
>>> d
deque([])
>>> d = deque(maxlen=None)
>>> d
deque([])
>>> d = deque(maxlen = 5)
>>> d = deque('python', maxlen = 5)
>>> d
deque(['y', 't', 'h', 'o', 'n'], maxlen=5)
>>> d = deque((2,5))
>>> d
deque([2, 5])
>>> d = deque((2,))
>>> d
deque([2])
# 其它
>>> d = deque('python')
>>> for elem in d:
print(elem.upper())
P
Y
T
H
O
N
>>> d.pop()
'n'
>>> d.popleft()
'p'
>>> d[0] # 支持indexed access
'y'
>>> d[-1]
'o'
>>> list(reversed(d)) # 支持reversed(d)，支持list()
['o', 'h', 't', 'y']
>>> d
deque(['y', 't', 'h', 'o']) # d没有发生变化
>>> 'h' in d #至此用in operator来检测membership
True
>>> d.rotate(-1)
>>> d
deque(['t', 'h', 'o', 'y'])
>>> deque(reversed(d))
deque(['y', 'o', 'h', 't'])
>>> d.clear()
>>> d.pop()
Traceback (most recent call last):
File "<pyshell#55>", line 1, in <module>
d.pop()
IndexError: pop from an empty deque
>>> d.extend('abc')
>>> d
deque(['a', 'b', 'c'])
>>> d.extendleft('abc')
>>> d
deque(['c', 'b', 'a', 'a', 'b', 'c'])
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