Fix #356: Improve RRCache performance.

Author: tkem

src/cachetools/__init__.py

@@ -288,16 +288,33 @@ class RRCache(Cache):
     def __init__(self, maxsize, choice=random.choice, getsizeof=None):
         Cache.__init__(self, maxsize, getsizeof)
         self.__choice = choice
+        self.__index = {}
+        self.__keys = []
 
     @property
     def choice(self):
         """The `choice` function used by the cache."""
         return self.__choice
 
+    def __setitem__(self, key, value, cache_setitem=Cache.__setitem__):
+        cache_setitem(self, key, value)
+        if key not in self.__index:
+            self.__index[key] = len(self.__keys)
+            self.__keys.append(key)
+
+    def __delitem__(self, key, cache_delitem=Cache.__delitem__):
+        cache_delitem(self, key)
+        index = self.__index.pop(key)
+        if index != len(self.__keys) - 1:
+            last = self.__keys[-1]
+            self.__keys[index] = last
+            self.__index[last] = index
+        self.__keys.pop()
+
     def popitem(self):
         """Remove and return a random `(key, value)` pair."""
         try:
-            key = self.__choice(list(self))
+            key = self.__choice(self.__keys)
         except IndexError:
             raise KeyError("%s is empty" % type(self).__name__) from None
         else:

tests/test_rr.py

@@ -1,3 +1,4 @@
+import random
 import unittest
 
 from cachetools import RRCache
@@ -32,3 +33,39 @@ def test_rr(self):
         self.assertEqual(3, cache[3])
         self.assertEqual(4, cache[4])
         self.assertNotIn(0, cache)
+
+    def test_rr_getsizeof(self):
+        cache = RRCache(maxsize=3, choice=min, getsizeof=lambda x: x)
+
+        cache[1] = 1
+        cache[2] = 2
+
+        self.assertEqual(len(cache), 2)
+        self.assertEqual(cache[1], 1)
+        self.assertEqual(cache[2], 2)
+
+        cache[3] = 3
+
+        self.assertEqual(len(cache), 1)
+        self.assertEqual(cache[3], 3)
+        self.assertNotIn(1, cache)
+        self.assertNotIn(2, cache)
+
+        with self.assertRaises(ValueError):
+            cache[4] = 4
+        self.assertEqual(len(cache), 1)
+        self.assertEqual(cache[3], 3)
+
+    def test_rr_bad_choice(self):
+        def bad_choice(seq):
+            raise ValueError("test error")
+
+        cache = RRCache(maxsize=2, choice=bad_choice)
+        cache[1] = 1
+        cache[2] = 2
+        with self.assertRaises(ValueError):
+            cache[3] = 3
+
+    def test_rr_default_choice(self):
+        cache = RRCache(maxsize=2)
+        self.assertIs(cache.choice, random.choice)