# HG changeset patch
# User Thierry Florac <tflorac@ulthar.net>
# Date 1333040738 -7200
# Node ID 72e3d386f4f631bcc7b154ab7d872bf97cb8806d
# Parent  5938c0d19c356715c4cb8509e70a2cb8506a3a74
Added cached properties and functions

diff -r 5938c0d19c35 -r 72e3d386f4f6 ztfy/utils/property.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ztfy/utils/property.py	Thu Mar 29 19:05:38 2012 +0200
@@ -0,0 +1,65 @@
+### -*- coding: utf-8 -*- ####################################################
+##############################################################################
+#
+# Copyright (c) 2012 Thierry Florac <tflorac AT ulthar.net>
+# All Rights Reserved.
+#
+# This software is subject to the provisions of the Zope Public License,
+# Version 2.1 (ZPL).  A copy of the ZPL should accompany this distribution.
+# THIS SOFTWARE IS PROVIDED "AS IS" AND ANY AND ALL EXPRESS OR IMPLIED
+# WARRANTIES ARE DISCLAIMED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF TITLE, MERCHANTABILITY, AGAINST INFRINGEMENT, AND FITNESS
+# FOR A PARTICULAR PURPOSE.
+#
+##############################################################################
+
+
+# import standard packages
+
+# import Zope3 interfaces
+
+# import local interfaces
+
+# import Zope3 packages
+
+# import local packages
+
+
+class cached(object):
+    """Custom property decorator to define a property or function
+    which is calculated only once
+       
+    When applied on a function, caching is based on input arguments
+    """
+
+    def __init__(self, function):
+        self._function = function
+        self._cache = {}
+
+    def __call__(self, *args):
+        try:
+            return self._cache[args]
+        except KeyError:
+            self._cache[args] = self._function(*args)
+            return self._cache[args]
+
+    def expire(self, *args):
+        del self._cache[args]
+
+
+class cached_property(object):
+    """A read-only @property decorator that is only evaluated once. The value is cached
+    on the object itself rather than the function or class; this should prevent
+    memory leakage.
+    """
+    def __init__(self, fget, doc=None):
+        self.fget = fget
+        self.__doc__ = doc or fget.__doc__
+        self.__name__ = fget.__name__
+        self.__module__ = fget.__module__
+
+    def __get__(self, obj, cls):
+        if obj is None:
+            return self
+        obj.__dict__[self.__name__] = result = self.fget(obj)
+        return result