[Zope3-checkins] SVN: Zope3/trunk/src/zope/cachedescriptors/property. Added a simple "read" property.

[Jim Fulton]

Log message for revision 38680:
  Added a simple "read" property.
  

Changed:
  U   Zope3/trunk/src/zope/cachedescriptors/property.py
  U   Zope3/trunk/src/zope/cachedescriptors/property.txt

-=-
Modified: Zope3/trunk/src/zope/cachedescriptors/property.py
===================================================================
--- Zope3/trunk/src/zope/cachedescriptors/property.py	2005-09-29 06:57:59 UTC (rev 38679)
+++ Zope3/trunk/src/zope/cachedescriptors/property.py	2005-09-29 09:12:36 UTC (rev 38680)
@@ -70,3 +70,16 @@
         inst.__dict__[name] = value
         
         return value
+
+class readproperty(object):
+
+    def __init__(self, func):
+        self.func = func
+
+    def __get__(self, inst, class_):
+        if inst is None:
+            return self
+
+        func = self.func
+        return func(inst)
+    

Modified: Zope3/trunk/src/zope/cachedescriptors/property.txt
===================================================================
--- Zope3/trunk/src/zope/cachedescriptors/property.txt	2005-09-29 06:57:59 UTC (rev 38679)
+++ Zope3/trunk/src/zope/cachedescriptors/property.txt	2005-09-29 09:12:36 UTC (rev 38680)
@@ -126,3 +126,30 @@
     >>> '%.2f' % point.diameter
     computing diameter
     '5.66'
+
+readproperties
+==============
+
+readproperties are like lazy computed attributes except that the
+attribute isn't set by the property:
+
+
+    >>> class Point:
+    ... 
+    ...     def __init__(self, x, y):
+    ...         self.x, self.y = x, y
+    ...
+    ...     def radius(self):
+    ...         print 'computing radius'
+    ...         return math.sqrt(self.x**2 + self.y**2)
+    ...     radius = property.readproperty(radius)
+
+    >>> point = Point(1.0, 2.0)   
+
+    >>> '%.2f' % point.radius
+    computing radius
+    '2.24'
+
+    >>> '%.2f' % point.radius
+    computing radius
+    '2.24'