LRUCache的实现原理及利用python实现的方法

class Entry:
 def __init__(self, hash_code, v, prev=None, next=None):
 self.hash_code = hash_code
 self.v = v
 self.prev = prev
 self.next = next

 def __str__(self):
 return "Entry{hash_code=%d, v=%s}" % (
  self.hash_code, self.v)
 __repr__ = __str__

class LRUCache:
 def __init__(self, max_size):
 self._max_size = max_size
 self._dict = dict()
 self._head = Entry(None, None)
 self._head.prev = self._head
 self._head.next = self._head

 def __setitem__(self, k, v):
 try:
  hash_code = hash(k)
 except TypeError:
  raise

 old_entry = self._dict.get(hash_code)
 new_entry = Entry(hash_code, v)
 self._dict[hash_code] = new_entry

 if old_entry:
  prev = old_entry.prev
  next = old_entry.next
  prev.next = next
  next.prev = prev

 head = self._head
 head_prev = self._head.prev
 head_next = self._head.next

 head.next = new_entry
 if head_prev is head:
  head.prev = new_entry
 head_next.prev = new_entry
 new_entry.prev = head
 new_entry.next = head_next

 if not old_entry and len(self._dict) > self._max_size:
  last_one = head.prev
  last_one.prev.next = head
  head.prev = last_one.prev
  self._dict.pop(last_one.hash_code)

 def __getitem__(self, k):
 entry = self._dict[hash(k)]
 head = self._head
 head_next = head.next
 prev = entry.prev
 next = entry.next

 if entry.prev is not head:
  if head.prev is entry:
  head.prev = prev
  head.next = entry

  head_next.prev = entry
  entry.prev = head
  entry.next = head_next

  prev.next = next
  next.prev = prev

 return entry.v

 def get_dict(self):
 return self._dict

if __name__ == "__main__":
 cache = LRUCache(2)
 inner_dict = cache.get_dict()

 cache[1] = 1
 assert inner_dict.keys() == [1], "test 1"
 cache[2] = 2
 assert sorted(inner_dict.keys()) == [1, 2], "test 2"
 cache[3] = 3
 assert sorted(inner_dict.keys()) == [2, 3], "test 3"
 cache[2]
 assert sorted(inner_dict.keys()) == [2, 3], "test 4"
 assert inner_dict[hash(2)].next.v == 3
 cache[4] = 4
 assert sorted(inner_dict.keys()) == [2, 4], "test 5"
 assert inner_dict[hash(4)].v == 4, "test 6"