我正在尝试用Python从头开始构建一个字典。我已经完成了大部分工作，但有一个小问题。首先，我要说的是，我正在使用内置的Python hash((来获取键的hash_result(键可以是int或str(，然后索引由dictionary的hash_resut%容量形成。如果密钥是一个字符串，则一切正常。只要关键字是整数，我的自定义字典就会中断。有时一切都正常，其他时候，当添加到字典时，键会得到哈希值0(例如(，但当在字典中搜索键时，同一个键会返回哈希值4(例如(。字典会返回KeyError，因为键映射在索引0而不是4。我相信，一开始，索引是通过hash(key(%capacity(例如4(来计算的，但一旦容量增加x2，函数hash(key(%capability(现在是8，因为x2(返回的索引就不同了，这就导致了问题。我在维基百科上看到了这个公式(hash(key(%容量(。我有兴趣了解这是否是我面临的问题，如果不是，是什么导致了这种不必要的行为，以及如何解决它。下面是我的代码：
class MyDictionary:
__LOAD_FACTOR_LIMIT = 0.75
__DEFAULT_CAPACITY = 4
def __init__(self):
self.__capacity = self.__DEFAULT_CAPACITY
self.__keys = [[] for i in range(self.__capacity)]
self.__values = [[] for i in range(self.__capacity)]
@property
def keys(self):
return [item for current_list in self.__keys for item in current_list]
@property
def values(self):
return [value for value_list in self.__values for value in value_list]
def __setitem__(self, key, value):
while self.__compute_load_factor() >= self.__LOAD_FACTOR_LIMIT:
self.__extend_dict()
index_hash = self.__hash_function(key)
if self.__is_key_in_dict(index_hash, key):
self.__set_value_to_an_existing_key(index_hash, key, value)
return
self.__set_value_to_a_new_key(index_hash, key, value)
def __getitem__(self, key):
index_hash = self.__hash_function(key)
if self.__is_key_in_dict(index_hash, key):
index_bucket = self.__get_index_bucket(index_hash, key)
return self.__values[index_hash][index_bucket]
raise KeyError('Key is not in dictionary!')
def __str__(self):
key_values = zip(self.keys, self.values)
result = '{' + ", ".join([f"{key}: {value}"
if isinstance(key, int) else f"'{key}': {value}"
for key, value in key_values]) + '}'
return result
def __hash_function(self, key):
index_hash = hash(key) % self.__capacity
return index_hash
def __is_key_in_dict(self, index_hash, key):
if key in self.__keys[index_hash]:
return True
return False
def __get_index_bucket(self, index_hash, key):
index_bucket = self.__keys[index_hash].index(key)
return index_bucket
def __extend_dict(self):
self.__keys += [[] for i in range(self.__capacity)]
self.__values += [[] for i in range(self.__capacity)]
self.__capacity *= 2
def __set_value_to_an_existing_key(self, index_hash, key, value):
index_bucket = self.__get_index_bucket(index_hash, key)
self.__values[index_hash][index_bucket] = value
def __set_value_to_a_new_key(self, index_hash, key, value):
self.__keys[index_hash].append(key)
self.__values[index_hash].append(value)
def __compute_load_factor(self):
k = len(self.__keys)
n = len([bucket for bucket in self.__keys if bucket])
return n / k
def get(self, key, return_value=None):
try:
index_hash = self.__hash_function(key)
index_bucket = self.__get_index_bucket(index_hash, key)
if self.__is_key_in_dict(index_hash, key):
return self.__keys[index_hash][index_bucket]
raise KeyError('Key is not in dictionary!')
except KeyError:
return return_value
def add(self):
pass
def pop(self):
pass
def clear(self):
self.__capacity = self.__DEFAULT_CAPACITY
self.__keys = [[] for i in range(self.__capacity)]
self.__values = [[] for i in range(self.__capacity)]
def items(self):
zipped_key_value = zip(self.keys, self.values)
return [item for item in zipped_key_value]
dictionary = MyDictionary()
dictionary.add()
dictionary[4] = 'hey'
dictionary['2'] = 'cya'
dictionary['4'] = 'welcome'
dictionary['5'] = 'welcome'
dictionary['32'] = 'heya'
dictionary['31'] = 'heya'
dictionary['36'] = 'heya'
dictionary['34'] = 'heya'
print(dictionary[4])
这是因为当负载超过阈值时，您通过调用__extend_dict方法来增加容量(存储在__capacity属性中(，这使得存储现有值的存储桶的索引不再有效，因为您总是通过取容量的模来导出索引。
因此，每次增加dict的容量时，都应该将现有的键和值重新插入到它们的新索引中：
def __extend_dict(self):
self.__capacity *= 2
new_keys = [[] for _ in range(self.__capacity)]
new_values = [[] for _ in range(self.__capacity)]
for keys, values in zip(self.__keys, self.__values):
for key, value in zip(keys, values):
index_hash = self.__hash_function(key)
new_keys[index_hash].append(key)
new_values[index_hash].append(value)
self.__keys = new_keys
self.__values = new_values
演示：https://replit.com/@blhsing/NewEnchantingPerimeter