--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/pyikriam/utils.py	Sat Nov 01 21:29:51 2008 +0800
@@ -0,0 +1,80 @@
+## \brief decorator is a class decorate another of another object.
+#
+# Access of attributes/methods that can not be found in an instance
+# of a class of this meta-class, decorator, are delegated to the backend
+# of the instance.
+#
+# A backend object always passed as first parameter when
+# instantiate an instance of a class with decorator as meta-class.
+# For example,
+# \code
+# class foo(object):
+#     __metaclass__ = decorator
+#
+# backend.data = 3
+# obj = foo(backend)
+# print obj.data
+# backend.data = 4
+# print obj.data
+# \endcode
+# it print out 3 and 4 respectively.
+# 
+class decorator(type):
+    def __init__(clz, name, base, dict):
+        super(decorator, clz).__init__(name, base, dict)
+        clz.__getattr__ = decorator.__dele_getattr
+        pass
+
+    @staticmethod
+    def set_backend(obj, backend):
+        obj.__backend = backend
+        pass
+
+    @staticmethod
+    def __dele_getattr(obj, name):
+        return getattr(obj.__backend, name)
+    pass
+
+
+## \brief Decorator to make functions or methods dynamic programming.
+#
+# dyna_prog result of functions or methods with their arguments as key.
+# It supposes result of a function always the same if the same arguments
+# are passed.  It cache result of cached function to avoid really calling
+# function every time.
+class dyna_prog(object):
+    class functor(object):
+        def __init__(self, instance, method):
+            self._method = method
+            self._instance = instance
+            self._cache = {}
+            pass
+
+        def __call__(self, *args):
+            try:
+                return self._cache[args]
+            except KeyError:
+                pass
+            instance = self._instance
+            result = self._method(instance, *args)
+            return self._cache.setdefault(args, result)
+
+        def clear(self):
+            self._cache.clear()
+        pass
+
+    def __init__(self, method):
+        super(dyna_prog, self).__init__()
+        self._method = method
+        self._functors = {}
+        pass
+    
+    def __get__(self, instance, owner):
+        try:
+            return self._functors[instance]
+        except KeyError:
+            pass
+        functor_o = dyna_prog.functor(instance, self._method)
+        return self._functors.setdefault(instance, functor_o)
+    pass
+