implementing some basic caching.

relates to #247.

bauble/test/test_utils.py

@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 #
 # Copyright (c) 2005,2006,2007,2008,2009 Brett Adams <brett@belizebotanic.org>
-# Copyright (c) 2012-2015 Mario Frasca <mario@anche.no>
+# Copyright (c) 2012-2016 Mario Frasca <mario@anche.no>
 #
 # This file is part of bauble.classic.
 #
@@ -19,10 +19,11 @@
 # along with bauble.classic. If not, see <http://www.gnu.org/licenses/>.
 
 import bauble.utils as utils
-from bauble.test import BaubleTestCase
+from unittest import TestCase
+
+
+class Utils(TestCase):
 
-class Utils(BaubleTestCase):
-
     def test_topological_sort_total(self):
         self.assertEqual(utils.topological_sort([1,2,3], [(2,1), (3,2)]), [3, 2, 1])
 
@@ -31,3 +32,58 @@ def test_topological_sort_partial(self):
 
     def test_topological_sort_loop(self):
         self.assertEqual(utils.topological_sort([1,2], [(2,1), (1,2)]), None)
+
+
+class CacheTest(TestCase):
+    def test_create_store_retrieve(self):
+        from bauble.utils import Cache
+        from functools import partial
+        invoked = []
+
+        def getter(x):
+            invoked.append(x)
+            return x
+
+        cache = Cache(2)
+        v = cache.get(1, partial(getter, 1))
+        self.assertEquals(v, 1)
+        self.assertEquals(invoked, [1])
+        v = cache.get(1, partial(getter, 1))
+        self.assertEquals(v, 1)
+        self.assertEquals(invoked, [1])
+
+    def test_respect_size(self):
+        from bauble.utils import Cache
+        from functools import partial
+        invoked = []
+
+        def getter(x):
+            invoked.append(x)
+            return x
+
+        cache = Cache(2)
+        cache.get(1, partial(getter, 1))
+        cache.get(2, partial(getter, 2))
+        cache.get(3, partial(getter, 3))
+        cache.get(4, partial(getter, 4))
+        self.assertEquals(invoked, [1, 2, 3, 4])
+        self.assertEquals(sorted(cache.storage.keys()), [3, 4])
+
+    def test_respect_timing(self):
+        from bauble.utils import Cache
+        from functools import partial
+        invoked = []
+
+        def getter(x):
+            invoked.append(x)
+            return x
+
+        cache = Cache(2)
+        cache.get(1, partial(getter, 1))
+        cache.get(2, partial(getter, 2))
+        cache.get(1, partial(getter, 1))
+        cache.get(3, partial(getter, 3))
+        cache.get(1, partial(getter, 1))
+        cache.get(4, partial(getter, 4))
+        self.assertEquals(invoked, [1, 2, 3, 4])
+        self.assertEquals(sorted(cache.storage.keys()), [1, 4])

bauble/utils/__init__.py

@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 #
 # Copyright (c) 2005,2006,2007,2008,2009 Brett Adams <brett@belizebotanic.org>
-# Copyright (c) 2015 Mario Frasca <mario@anche.no>
+# Copyright (c) 2015-2016 Mario Frasca <mario@anche.no>
 #
 # This file is part of bauble.classic.
 #
@@ -125,6 +125,39 @@ def read_local_url(self):
                 self.loader.write(piece)
 
 
+class Cache:
+    '''a simple class for caching images
+
+    you instantiate a size 10 cache like this:
+    >>> cache = ImageCache(10)
+
+    if `getter` is a function that returns a picture, you don't immediately
+    invoke it, you use the cache like this:
+    >>> image = cache.get(name, getter)
+
+    internally, the cache is stored in a dictionary, the key is the name of
+    the image, the value is a pair with first the timestamp of the last usage
+    of that key and second the value.
+    '''
+
+    def __init__(self, size):
+        self.size = size
+        self.storage = {}
+
+    def get(self, key, getter):
+        if key in self.storage:
+            value = self.storage[key][1]
+        else:
+            if len(self.storage) == self.size:
+                # remove the oldest entry
+                k = min(zip(self.storage.values(), self.storage.keys()))[1]
+                del self.storage[k]
+            value = getter()
+        import time
+        self.storage[key] = time.time(), value
+        return value
+
+
 def find_dependent_tables(table, metadata=None):
     '''
     Return an iterator with all tables that depend on table.  The