Python优雅扩展字典Dict的三种方法详解

class EnhancedDict(dict):
    """增强型字典，提供大小写不敏感的键访问"""
    
    def __getitem__(self, key):
        return super().__getitem__(key.lower())
    
    def __setitem__(self, key, value):
        super().__setitem__(key.lower(), value)

from collections import UserDict

class HistoryDict(UserDict):
    """记录修改历史的字典"""
    
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.history = []
    
    def __setitem__(self, key, value):
        self.history.append(f"Set {key} = {value}")
        super().__setitem__(key, value)

from collections.abc import MutableMapping

class LRUCache(MutableMapping):
    """最近最少使用缓存实现"""
    
    def __init__(self, maxsize=128):
        self._cache = {}
        self._maxsize = maxsize
        self._order = []
    
    # 必须实现抽象方法
    def __getitem__(self, key):
        # 实现细节...
        pass
    
    def __setitem__(self, key, value):
        # 实现细节...
        pass
    
    def __delitem__(self, key):
        # 实现细节...
        pass
    
    def __iter__(self):
        # 实现细节...
        pass
    
    def __len__(self):
        # 实现细节...
        pass

class DefaultDict(dict):
    """提供默认值的字典"""
    
    def __init__(self, default_factory=None, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.default_factory = default_factory
    
    def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        value = self.default_factory()
        self[key] = value
        return value

class TypedDict(dict):
    """限制键值类型的字典"""
    
    def __init__(self, key_type=None, value_type=None, *args, **kwargs):
        self.key_type = key_type
        self.value_type = value_type
        super().__init__(*args, **kwargs)
    
    def __setitem__(self, key, value):
        if self.key_type and not isinstance(key, self.key_type):
            raise TypeError(f"Key must be {self.key_type}")
        if self.value_type and not isinstance(value, self.value_type):
            raise TypeError(f"Value must be {self.value_type}")
        super().__setitem__(key, value)

import json
import os

class PersistentDict(dict):
    """自动保存到文件的字典"""
    
    def __init__(self, filename, *args, **kwargs):
        self.filename = filename
        if os.path.exists(filename):
            with open(filename, 'r') as f:
                data = json.load(f)
            super().__init__(data)
        else:
            super().__init__(*args, **kwargs)
    
    def sync(self):
        """将字典内容同步到文件"""
        with open(self.filename, 'w') as f:
            json.dump(dict(self), f)
    
    def __setitem__(self, key, value):
        super().__setitem__(key, value)
        self.sync()
    
    def __delitem__(self, key):
        super().__delitem__(key)
        self.sync()