python - 'maxlen' 对象的属性 'collections.deque' 不可写

Question

class TailDeque(collections.deque):
    '''Implementation of deque with limited maxlen support for Python 2.5.'''
    def __init__(self, iterable=None, maxlen=-1):
        super(TailDeque, self).__init__([])
        self.maxlen = maxlen
        if iterable is not None:
            self.extend(iterable)

    def extend(self, iterable):
        for item in iterable:
            self.append(item)

    def extendleft(self, iterable):
        for item in iterable:
            self.appendleft(item)

    def appendleft(self, item):
        if len(self) == self.maxlen:
            self.pop()
        super(TailDeque, self).appendleft(item)    

    def append(self, item):
        if len(self) == self.maxlen:
            self.popleft()
        super(TailDeque, self).append(item)
logQueue = TailDeque(maxlen=20)

有人可以解释并告诉我如何为 python 3.4 执行此操作吗？

我总是得到

AttributeError: attribute 'maxlen' of 'collections.deque' objects is not writable

https://docs.python.org/2/library/collections.html#deque-objects

Answer 1

maxlen参数在2.6和3.0中被添加到collections.deque中。 (从参数设置的只读 maxlen 属性是在 2.7 和 3.1 中添加的。)您发布的代码适用于 2.5 作为部分替代。对于 2.6+ 和 3.1+，你应该只使用 collections.deque 而不必担心部分向后移植。如果您正在编写支持 2.5 到 2.7 的代码，则在 2.5 上运行时应将 collections.deque 替换为其包装器。类似的东西

import sys

major = sys.version[0:3]

if major >= '2.6':
    from collections import deque
elif major == '2.5':
    from myutils import TailDeque as deque
else:
    raise MyException('This app requires 2.5 or later.')