Python OrderedDict有序字典详解 - move_to_end与LRU缓存实现

from collections import OrderedDict

# 创建OrderedDict
od = OrderedDict()
od = OrderedDict([('a', 1), ('b', 2), ('c', 3)])
od = OrderedDict(a=1, b=2, c=3)

from collections import OrderedDict

# 创建并验证顺序
od = OrderedDict()
od["banana"] = 3
od["apple"] = 4
od["pear"] = 1
od["orange"] = 2

print("插入顺序:")
for key, value in od.items():
    print(f"  {key}: {value}")

# move_to_end：移动到末尾
od.move_to_end("apple")
print(f"\napple移到末尾: {list(od.keys())}")

# move_to_end：移动到开头
od.move_to_end("pear", last=False)
print(f"pear移到开头: {list(od.keys())}")

# popitem：弹出末尾
key, value = od.popitem()
print(f"\n弹出末尾: {key}={value}")
print(f"剩余: {list(od.keys())}")

# popitem：弹出开头
key, value = od.popitem(last=False)
print(f"弹出开头: {key}={value}")
print(f"剩余: {list(od.keys())}")

插入顺序:
  banana: 3
  apple: 4
  pear: 1
  orange: 2

apple移到末尾: ['banana', 'pear', 'orange', 'apple']
pear移到开头: ['pear', 'banana', 'orange', 'apple']

弹出末尾: apple=4
剩余: ['pear', 'banana', 'orange']

弹出开头: pear=1
剩余: ['banana', 'orange']

from collections import OrderedDict

class LRUCache:
    """LRU（最近最少使用）缓存"""

    def __init__(self, capacity):
        self.capacity = capacity
        self.cache = OrderedDict()

    def get(self, key):
        """获取缓存值，存在则移到末尾"""
        if key not in self.cache:
            return -1
        self.cache.move_to_end(key)
        return self.cache[key]

    def put(self, key, value):
        """添加缓存，超出容量则移除最久未使用的"""
        if key in self.cache:
            self.cache.move_to_end(key)
        self.cache[key] = value
        if len(self.cache) > self.capacity:
            self.cache.popitem(last=False)

    def display(self):
        print(f"缓存({len(self.cache)}/{self.capacity}): {list(self.cache.items())}")

# 使用示例
cache = LRUCache(3)
cache.put("a", 1)
cache.put("b", 2)
cache.put("c", 3)
cache.display()

# 访问a，a移到末尾
cache.get("a")
cache.display()

# 添加d，超出容量，移除最久未使用的b
cache.put("d", 4)
cache.display()

# 访问c
cache.get("c")
cache.display()

# 添加e，移除a
cache.put("e", 5)
cache.display()

缓存(3/3): [('a', 1), ('b', 2), ('c', 3)]
缓存(3/3): [('b', 2), ('c', 3), ('a', 1)]
缓存(3/3): [('c', 3), ('a', 1), ('d', 4)]
缓存(3/3): [('a', 1), ('d', 4), ('c', 3)]
缓存(3/3): [('d', 4), ('c', 3), ('e', 5)]

from collections import OrderedDict

class OrderedConfig:
    """有序配置管理器"""

    def __init__(self):
        self._config = OrderedDict()

    def set(self, key, value):
        """设置配置项"""
        self._config[key] = value

    def get(self, key, default=None):
        """获取配置项"""
        return self._config.get(key, default)

    def reorder(self, key, position):
        """调整配置项顺序"""
        if key not in self._config:
            return False

        if position == "first":
            self._config.move_to_end(key, last=False)
        elif position == "last":
            self._config.move_to_end(key, last=True)
        return True

    def display(self):
        """显示配置"""
        print("配置项（按顺序）:")
        for i, (key, value) in enumerate(self._config.items(), 1):
            print(f"  {i}. {key} = {value}")

# 使用示例
config = OrderedConfig()
config.set("database", "mysql")
config.set("port", 3306)
config.set("host", "localhost")
config.set("charset", "utf8")
config.set("timeout", 30)

print("初始配置:")
config.display()

# 将host移到第一位
config.reorder("host", "first")
print("\nhost移到第一位:")
config.display()

# 将timeout移到最后
config.reorder("timeout", "last")
print("\ntimeout移到最后:")
config.display()

初始配置:
配置项（按顺序）:
  1. database = mysql
  2. port = 3306
  3. host = localhost
  4. charset = utf8
  5. timeout = 30

host移到第一位:
配置项（按顺序）:
  1. host = localhost
  2. database = mysql
  3. port = 3306
  4. charset = utf8
  5. timeout = 30

timeout移到最后:
配置项（按顺序）:
  1. host = localhost
  2. database = mysql
  3. port = 3306
  4. charset = utf8
  5. timeout = 30