[pitivi: 3/6] new module: thumbnailcache, with unit test

[Edward Hervey <edwardrv src gnome org>]

commit 10aea80b5784141d7e0b2d5f06fc8806d4073682
Author: Brandon Lewis <brandon_lewis berkeley edu>
Date:   Fri Mar 6 18:11:32 2009 -0800

    new module: thumbnailcache, with unit test
---
 pitivi/thumbnailcache.py |   64 ++++++++++++++++++++++++++++++++++++++++++++++
 tests/test_cache.py      |   29 +++++++++++++++++++++
 2 files changed, 93 insertions(+), 0 deletions(-)

diff --git a/pitivi/thumbnailcache.py b/pitivi/thumbnailcache.py
new file mode 100644
index 0000000..a7e3fcc
--- /dev/null
+++ b/pitivi/thumbnailcache.py
@@ -0,0 +1,64 @@
+#!/usr/bin/python
+# PiTiVi , Non-linear video editor
+#
+#       thumbnailcache.py
+#
+# Copyright (c) 2009, Brandon Lewis (brandon_lewis berkeley edu)
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this program; if not, write to the
+# Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+# Boston, MA 02111-1307, USA.
+
+"""
+Dictionary-Like object for caching of thumbnails.
+"""
+
+import collections
+
+class ThumbnailCache(object):
+
+    """Caches thumbnails by key using LRU policy, implemented with heapq"""
+
+    def __init__(self, size=100):
+        object.__init__(self)
+        self.queue = collections.deque()
+        self.cache = {}
+        self.hits = 0
+        self.misses = 0
+        self.size = size
+
+    def __contains__(self, key):
+        if key in self.cache:
+            self.hits += 1
+            return True
+        self.misses += 1
+        return False
+
+    def __getitem__(self, key):
+        if key in self.cache:
+            # I guess this is why LRU is considered expensive
+            self.queue.remove(key)
+            self.queue.append(key)
+            return self.cache[key]
+        raise KeyError(key)
+
+    def __setitem__(self, key, value):
+        self.cache[key] = value
+        self.queue.append(key)
+        if len(self.cache) > self.size:
+            self.ejectLRU()
+
+    def ejectLRU(self):
+        key = self.queue.popleft()
+        del self.cache[key]
diff --git a/tests/test_cache.py b/tests/test_cache.py
new file mode 100644
index 0000000..bf18606
--- /dev/null
+++ b/tests/test_cache.py
@@ -0,0 +1,29 @@
+import unittest
+import pitivi
+from common import TestCase
+from pitivi.thumbnailcache import ThumbnailCache
+
+class CacheTest(TestCase):
+    """
+    Basic test to create the proper creation of the Pitivi object
+    """
+
+    def testCache(self):
+        c = ThumbnailCache(size=32)
+        for i in xrange(0, 64):
+            c[i] = i
+        assert len(c.cache) == 32
+        assert not 31 in c
+        assert 32 in c
+        
+        # touch the LRU item, and then add something to the queue
+        # the item should still remain in the queue
+
+        c[32]
+        c[65] = 65
+
+        assert 32 in c
+        assert not 33 in c
+
+if __name__ == "__main__":
+    unittest.main()