Python中Dict两种实现的原理详解

array = [
	[
    # 分别为key, hash值， 数值
		('key1', 123, 123),
		('key2', 123, 123)
	],
	[
		('key3', 123, 123)
	]
]

arrray = [None, None, None, None, True, True, True, True]

array = [
	[],
	[123456, "key1", 1],
	[],
	[],
	[],
	[234567, "key2", 2],
	[],
	[]
]

# 初始的结构
# -1代表还未插入数据
array_1 = [-1, -1, -1, -1, -1, -1, -1, -1]
array_2 = []


# 插入值后, 他就会变为:
array_1 = [-1, 0, -1, -1, -1, 1, -1, -1]
array_2 = [
	[123456, "key1", 1],
	[234567, "key2", 2],
]

from typing import Any, Iterable, List, Optional, Tuple


class CustomerDict(object):

    def __init__(self):
        self._init_seed: int = 3  # 容量因子
        self._init_length: int = 2 ** self._init_seed  # 初始化数组大小
        self._load_factor: float = 2 / 3  # 扩容因子
        self._index_array: List[int] = [-1 for _ in range(self._init_length)]  # 存放下标的数组
        self._data_array: List[Optional[Tuple[int, Any, Any]]] = []  # 存放数据的数组
        self._used_count: int = 0  # 目前用的量
        self._delete_count: int = 0  # 被标记删除的量

    def _create_new(self):
        """扩容函数"""
        self._init_seed += 1  # 增加容量因子
        self._init_length = 2 ** self._init_seed
        old_data_array: List[Tuple[int, Any, Any]] = self._data_array
        self._index_array: List[int] = [-1 for _ in range(self._init_length)]
        self._data_array: List[Tuple[int, Any, Any]] = []
        self._used_count = 0
        self._delete_count = 0

        # 这里只是简单实现, 实际上只需要搬运一半的数据
        for item in old_data_array:
            if item is not None:
                self.__setitem__(item[1], item[2])

    def _get_next(self, index: int):
        """计算冲突的下一跳，如果下标对应的值冲突了, 需要计算下一跳的下标"""
        return ((5*index) + 1) % self._init_length

    def _core(self, key: Any, default_value: Optional[Any] = None) -> Tuple[int, Any, int]:
        """获取数据或者得到可以放新数据的方法, 返回值是index_array的索引, 数据, data_array的索引"""
        index: int = hash(key) % (self._init_length - 1)
        while True:
            data_index: int = self._index_array[index]
            # 如果是-1则代表没有数据
            if data_index == -1:
                break
            # 如果是-2则代表之前有数据则不过被删除了
            elif data_index == -2:
                index = self._get_next(index)
                continue

            _, new_key, default_value = self._data_array[data_index]
            # 判断是不是对应的key
            if key != new_key:
                index = self._get_next(index)
            else:
                break
        return index, default_value, data_index

    def __getitem__(self, key: Any) -> Any:
        _, value, data_index = self._core(key)
        if data_index == -1:
            raise KeyError(key)
        return value

    def __setitem__(self, key: Any, value: Any) -> None:
        if (self._used_count / self._init_length) > self._load_factor:
            self._create_new()
        index, _, _ = self._core(key)

        self._index_array[index] = self._used_count
        self._data_array.append((hash(key), key, value))
        self._used_count += 1

    def __delitem__(self, key: Any) -> None:
        index, _, data_index = self._core(key)
        if data_index == -1:
            raise KeyError(key)
        self._index_array[index] = -2
        self._data_array[data_index] = None
        self._delete_count += 1

    def __len__(self) -> int:
        return self._used_count - self._delete_count

    def __iter__(self) -> Iterable:
        return iter(self._data_array)
    
    def __str__(self) -> str:
        return str({item[1]: item[2] for item in self._data_array if item is not None})

    def keys(self) -> List[Any]:
        """模拟实现keys方法"""
        return [item[1] for item in self._data_array if item is not None]

    def values(self) -> List[Any]:
        """模拟实现values方法"""
        return [item[2] for item in self._data_array if item is not None]

    def items(self) -> List[Tuple[Any, Any]]:
        """模拟实现items方法"""
        return [(item[1], item[2]) for item in self._data_array if item is not None]


if __name__ == '__main__':
    customer_dict: CustomerDict = CustomerDict()
    customer_dict["demo_1"] = "a"
    customer_dict["demo_2"] = "b"
    assert len(customer_dict) == 2

    del customer_dict["demo_1"]
    del customer_dict["demo_2"]
    assert len(customer_dict) == 0

    for i in range(30):
        customer_dict[i] = i
    assert len(customer_dict) == 30

    customer_dict_value_list: List[Any] = customer_dict.values()
    for i in range(30):
        assert i == customer_dict[i]

    for i in range(30):
        assert customer_dict[i] == i
        del customer_dict[i]
    assert len(customer_dict) == 0