如何从字典中删除最旧的元素? [英] How to remove the oldest element from a dictionary?

问题描述

我想知道删除字典中最旧元素的最佳方法，以便控制最大字典大小.

I would like to know the best way to remove the oldest element in a dictionary in order to control the maximum dictionary size.

示例:

MAXSIZE = 4
dict = {}
def add(key,value):
  if len(dict) == MAXSIZE:
    old = get_oldest_key() # returns the key to the oldest item
    del dict[old]
  dict[key] = value

add('a','1') # {'a': '1'}
add('b','2') # {'a': '1', 'b': '2'}
add('c','3') # {'a': '1', 'c': '3', 'b': '2'}
add('d','4') # {'a': '1', 'c': '3', 'b': '2', 'd': '4'}
add('e','5') # {'c': '3', 'b': '2', 'e': '5', 'd': '4'}

这清楚吗?

编辑:忘记了len(dict)落后一项.

推荐答案

字典不保留顺序，因此您无法确定首先添加了哪个元素.您可以将字典与其键列表结合起来以保持顺序.

Dictionaries don't preserve order, so you can't tell which element had been added first. You could combine the dictionary with a list of it's keys to preserve order.

这是 activestate食谱，用于执行此操作的有序字典.

Here's an activestate recipe for an ordered dict that does just this.

还有 PEP-0372 与此

There's also PEP-0372 with this patch for an odict class.

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