Simpler and faster LRUCache implementation

darc/lrucache.py

@@ -3,78 +3,37 @@
 import unittest
 
 
-class LRUCache(DictMixin):
-    """Heap queue based Least Recently Used Cache implementation
-    """
+class LRUCache(dict):
 
-    class Node(object):
-        """Internal cache node
-        """
-        __slots__ = ('key', 'value', 't')
-
-        def __init__(self, key, value, t):
-            self.key = key
-            self.value = value
-            self.t = t
-
-        def __cmp__(self, other):
-            return cmp(self.t, other.t)
-
-    def __init__(self, size):
-        self.size = size
-        self._t = 0
-        self.clear()
-
-    def clear(self):
-        self._heap = []
-        self._dict = {}
+    def __init__(self, capacity):
+        super(LRUCache, self).__init__()
+        self._lru = []
+        self._capacity = capacity
 
     def __setitem__(self, key, value):
-        self._t += 1
         try:
-            node = self._dict[key]
-            node.value = value
-            node.t = self._t
-            heapify(self._heap)
-        except KeyError:
-            node = self.Node(key, value, self._t)
-            self._dict[key] = node
-            if len(self) < self.size:
-                heappush(self._heap, node)
-            else:
-                old = heapreplace(self._heap, node)
-                del self._dict[old.key]
+            self._lru.remove(key)
+        except ValueError:
+            pass
+        self._lru.append(key)
+        while len(self._lru) > self._capacity:
+            del self[self._lru[0]]
+        return super(LRUCache, self).__setitem__(key, value)
 
     def __getitem__(self, key):
-        node = self._dict[key]
-        self[key] = node.value
-        return node.value
+        try:
+            self._lru.remove(key)
+            self._lru.append(key)
+        except ValueError:
+            pass
+        return super(LRUCache, self).__getitem__(key)
 
     def __delitem__(self, key):
-        node = self._dict[key]
-        del self._dict[key]
-        self._heap.remove(node)
-        heapify(self._heap)
-
-    def __iter__(self):
-        copy = self._heap[:]
-        while copy:
-            yield heappop(copy).key
-
-    def iteritems(self):
-        copy = self._heap[:]
-        while copy:
-            node = heappop(copy)
-            yield node.key, node.value
-
-    def keys(self):
-        return self._dict.keys()
-
-    def __contains__(self, key):
-        return key in self._dict
-
-    def __len__(self):
-        return len(self._heap)
+        try:
+            self._lru.remove(key)
+        except ValueError:
+            pass
+        return super(LRUCache, self).__delitem__(key)
 
 
 class LRUCacheTestCase(unittest.TestCase):
@@ -85,8 +44,8 @@ def test(self):
         for i, x in enumerate('abc'):
             c[x] = i
         self.assertEqual(len(c), 2)
-        self.assertEqual(list(c), ['b', 'c'])
-        self.assertEqual(list(c.iteritems()), [('b', 1), ('c', 2)])
+        self.assertEqual(set(c), set(['b', 'c']))
+        self.assertEqual(set(c.iteritems()), set([('b', 1), ('c', 2)]))
         self.assertEqual(False, 'a' in c)
         self.assertEqual(True, 'b' in c)
         self.assertRaises(KeyError, lambda: c['a'])