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GeezerVison is showing github.com — Python/other/lfu_cache.py at master · https-github-com-nzysoft/Python Expand file tree/ Copy pathlfu_cache.pyMore file actions 316 lines (248 loc) · 9.56 KB / Copy pathlfu_cache.pyFile metadata and controls316 lines (248 loc) · 9.56 KB 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 from __future__ import annotations from collections.abc import Callable from typing import Generic, TypeVar T = TypeVar("T") U = TypeVar("U") class DoubleLinkedListNode(Generic[T, U]): """ Double Linked List Node built specifically for LFU Cache >>> node = DoubleLinkedListNode(1,1) >>> node Node: key: 1, val: 1, freq: 0, has next: False, has prev: False """ def __init__(self, key: T | None, val: U | None): self.key = key self.val = val self.freq: int = 0 self.next: DoubleLinkedListNode[T, U] | None = None self.prev: DoubleLinkedListNode[T, U] | None = None def __repr__(self) -> str: return "Node: key: {}, val: {}, freq: {}, has next: {}, has prev: {}".format( self.key, self.val, self.freq, self.next is not None, self.prev is not None ) class DoubleLinkedList(Generic[T, U]): """ Double Linked List built specifically for LFU Cache >>> dll: DoubleLinkedList = DoubleLinkedList() >>> dll DoubleLinkedList, Node: key: None, val: None, freq: 0, has next: True, has prev: False, Node: key: None, val: None, freq: 0, has next: False, has prev: True >>> first_node = DoubleLinkedListNode(1,10) >>> first_node Node: key: 1, val: 10, freq: 0, has next: False, has prev: False >>> dll.add(first_node) >>> dll DoubleLinkedList, Node: key: None, val: None, freq: 0, has next: True, has prev: False, Node: key: 1, val: 10, freq: 1, has next: True, has prev: True, Node: key: None, val: None, freq: 0, has next: False, has prev: True >>> # node is mutated >>> first_node Node: key: 1, val: 10, freq: 1, has next: True, has prev: True >>> second_node = DoubleLinkedListNode(2,20) >>> second_node Node: key: 2, val: 20, freq: 0, has next: False, has prev: False >>> dll.add(second_node) >>> dll DoubleLinkedList, Node: key: None, val: None, freq: 0, has next: True, has prev: False, Node: key: 1, val: 10, freq: 1, has next: True, has prev: True, Node: key: 2, val: 20, freq: 1, has next: True, has prev: True, Node: key: None, val: None, freq: 0, has next: False, has prev: True >>> removed_node = dll.remove(first_node) >>> assert removed_node == first_node >>> dll DoubleLinkedList, Node: key: None, val: None, freq: 0, has next: True, has prev: False, Node: key: 2, val: 20, freq: 1, has next: True, has prev: True, Node: key: None, val: None, freq: 0, has next: False, has prev: True >>> # Attempt to remove node not on list >>> removed_node = dll.remove(first_node) >>> removed_node is None True >>> # Attempt to remove head or rear >>> dll.head Node: key: None, val: None, freq: 0, has next: True, has prev: False >>> dll.remove(dll.head) is None True >>> # Attempt to remove head or rear >>> dll.rear Node: key: None, val: None, freq: 0, has next: False, has prev: True >>> dll.remove(dll.rear) is None True """ def __init__(self) -> None: self.head: DoubleLinkedListNode[T, U] = DoubleLinkedListNode(None, None) self.rear: DoubleLinkedListNode[T, U] = DoubleLinkedListNode(None, None) self.head.next, self.rear.prev = self.rear, self.head def __repr__(self) -> str: rep = ["DoubleLinkedList"] node = self.head while node.next is not None: rep.append(str(node)) node = node.next rep.append(str(self.rear)) return ",\n ".join(rep) def add(self, node: DoubleLinkedListNode[T, U]) -> None: """ Adds the given node at the tail of the list and shifting it to proper position """ previous = self.rear.prev # All nodes other than self.head are guaranteed to have non-None previous assert previous is not None previous.next = node node.prev = previous self.rear.prev = node node.next = self.rear node.freq += 1 self._position_node(node) def _position_node(self, node: DoubleLinkedListNode[T, U]) -> None: """ Moves node forward to maintain invariant of sort by freq value """ while node.prev is not None and node.prev.freq > node.freq: # swap node with previous node previous_node = node.prev node.prev = previous_node.prev previous_node.next = node.prev node.next = previous_node previous_node.prev = node def remove( self, node: DoubleLinkedListNode[T, U] ) -> DoubleLinkedListNode[T, U] | None: """ Removes and returns the given node from the list Returns None if node.prev or node.next is None """ if node.prev is None or node.next is None: return None node.prev.next = node.next node.next.prev = node.prev node.prev = None node.next = None return node class LFUCache(Generic[T, U]): """ LFU Cache to store a given capacity of data. Can be used as a stand-alone object or as a function decorator. >>> cache = LFUCache(2) >>> cache.put(1, 1) >>> cache.put(2, 2) >>> cache.get(1) 1 >>> cache.put(3, 3) >>> cache.get(2) is None True >>> cache.put(4, 4) >>> cache.get(1) is None True >>> cache.get(3) 3 >>> cache.get(4) 4 >>> cache CacheInfo(hits=3, misses=2, capacity=2, current_size=2) >>> @LFUCache.decorator(100) ... def fib(num): ... if num in (1, 2): ... return 1 ... return fib(num - 1) + fib(num - 2) >>> for i in range(1, 101): ... res = fib(i) >>> fib.cache_info() CacheInfo(hits=196, misses=100, capacity=100, current_size=100) """ # class variable to map the decorator functions to their respective instance decorator_function_to_instance_map: dict[Callable[[T], U], LFUCache[T, U]] = {} def __init__(self, capacity: int): self.list: DoubleLinkedList[T, U] = DoubleLinkedList() self.capacity = capacity self.num_keys = 0 self.hits = 0 self.miss = 0 self.cache: dict[T, DoubleLinkedListNode[T, U]] = {} def __repr__(self) -> str: """ Return the details for the cache instance [hits, misses, capacity, current_size] """ return ( f"CacheInfo(hits={self.hits}, misses={self.miss}, " f"capacity={self.capacity}, current_size={self.num_keys})" ) def __contains__(self, key: T) -> bool: """ >>> cache = LFUCache(1) >>> 1 in cache False >>> cache.put(1, 1) >>> 1 in cache True """ return key in self.cache def get(self, key: T) -> U | None: """ Returns the value for the input key and updates the Double Linked List. Returns Returns None if key is not present in cache """ if key in self.cache: self.hits += 1 value_node: DoubleLinkedListNode[T, U] = self.cache[key] node = self.list.remove(self.cache[key]) assert node == value_node # node is guaranteed not None because it is in self.cache assert node is not None self.list.add(node) return node.val self.miss += 1 return None def put(self, key: T, value: U) -> None: """ Sets the value for the input key and updates the Double Linked List """ if key not in self.cache: if self.num_keys >= self.capacity: # delete first node when over capacity first_node = self.list.head.next # guaranteed to have a non-None first node when num_keys > 0 # explain to type checker via assertions assert first_node is not None assert first_node.key is not None assert self.list.remove(first_node) is not None # first_node guaranteed to be in list del self.cache[first_node.key] self.num_keys -= 1 self.cache[key] = DoubleLinkedListNode(key, value) self.list.add(self.cache[key]) self.num_keys += 1 else: node = self.list.remove(self.cache[key]) assert node is not None # node guaranteed to be in list node.val = value self.list.add(node) @classmethod def decorator( cls: type[LFUCache[T, U]], size: int = 128 ) -> Callable[[Callable[[T], U]], Callable[..., U]]: """ Decorator version of LFU Cache Decorated function must be function of T -> U """ def cache_decorator_inner(func: Callable[[T], U]) -> Callable[..., U]: def cache_decorator_wrapper(*args: T) -> U: if func not in cls.decorator_function_to_instance_map: cls.decorator_function_to_instance_map[func] = LFUCache(size) result = cls.decorator_function_to_instance_map[func].get(args[0]) if result is None: result = func(*args) cls.decorator_function_to_instance_map[func].put(args[0], result) return result def cache_info() -> LFUCache[T, U]: return cls.decorator_function_to_instance_map[func] setattr(cache_decorator_wrapper, "cache_info", cache_info) # noqa: B010 return cache_decorator_wrapper return cache_decorator_inner if __name__ == "__main__": import doctest doctest.testmod() |
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