1 files changed, 97 insertions, 0 deletions
diff --git a/cache.py b/cache.py
new file mode 100644
index 0000000..9e3c994
--- /dev/null
+++ b/cache.py
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+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free Software
+# Foundation; either version 2 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 General Public License for more details.
+#
+# You should have received a copy of the GNU 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.
+""" Copyright (c) 2002-2003 LOGILAB S.A. (Paris, FRANCE).
+ http://www.logilab.fr/ -- mailto:contact@logilab.fr
+
+ Cache module, with a least recently used algorithm for the management of the
+ deletion of entries.
+"""
+
+__revision__ = '$Id: cache.py,v 1.8 2003-10-31 14:18:31 syt Exp $'
+
+
+class Cache:
+    """ a dictionnary like cache
+
+    inv:
+        len(self._usage) <= self.size
+        len(self.data) <= self.size
+    """
+    
+    def __init__(self, size=100):
+        self.data = {}
+        self.size = size
+        self._usage = []
+
+    def __repr__(self):
+        return repr(self.data)
+
+    def __len__(self):
+        return len(self.data)
+
+    def _update_usage(self, key):
+        # Special case : cache's size = 0 !
+        if self.size <= 0:
+            return
+        
+        if not self._usage:
+            self._usage.append(key)
+        
+        if self._usage[-1] != key:
+            try:
+                self._usage.remove(key)
+            except ValueError:
+                # we are inserting a new key
+                # check the size of the dictionnary
+                # and remove the oldest item in the cache
+                if self.size and len(self._usage) >= self.size:
+                    del self.data[self._usage[0]]
+                    del self._usage[0]
+            self._usage.append(key)
+
+            
+    def __getitem__(self, key):
+        value = self.data[key]
+        self._update_usage(key)
+        return value
+    
+    def __setitem__(self, key, item):
+        # Just make sure that size > 0 before inserting a new item in the cache
+        if self.size > 0:
+            self.data[key] = item
+        self._update_usage(key)
+        
+    def __delitem__(self, key):
+        # If size <= 0, then we don't have anything to do
+        # XXX FIXME : Should we let the 'del' raise a KeyError ?
+        if self.size > 0:
+            del self.data[key]
+            self._usage.remove(key)
+        
+    def clear(self):
+        self.data.clear()
+        self._usage = []
+
+    def keys(self):
+        return self.data.keys()
+
+    def items(self):
+        return self.data.items()
+
+    def values(self):
+        return self.data.values()
+
+    def has_key(self, key):
+        return self.data.has_key(key)
+
+