refactored lazy properties little bit for ThreadecLocal to work better

rhodecode/lib/vcs/utils/lazy.py

@@ -1,45 +1,62 b''
+class _Missing(object):
+
+    def __repr__(self):
+        return 'no value'
+
+    def __reduce__(self):
+        return '_missing'
+
+_missing = _Missing()
+
+
 class LazyProperty(object):
     """
     Decorator for easier creation of ``property`` from potentially expensive to
     calculate attribute of the class.
 
     Usage::
 
       class Foo(object):
           @LazyProperty
           def bar(self):
               print 'Calculating self._bar'
               return 42
 
     Taken from http://blog.pythonisito.com/2008/08/lazy-descriptors.html and
     used widely.
     """
 
     def __init__(self, func):
         self._func = func
         self.__module__ = func.__module__
         self.__name__ = func.__name__
         self.__doc__ = func.__doc__
 
     def __get__(self, obj, klass=None):
         if obj is None:
             return self
-        result = obj.__dict__[self.__name__] = self._func(obj)
-        return result
+        value = obj.__dict__.get(self.__name__, _missing)
+        if value is _missing:
+            value = self._func(obj)
+            obj.__dict__[self.__name__] = value
+        return value
 
 import threading
 
 
 class ThreadLocalLazyProperty(LazyProperty):
     """
     Same as above but uses thread local dict for cache storage.
     """
 
     def __get__(self, obj, klass=None):
         if obj is None:
             return self
         if not hasattr(obj, '__tl_dict__'):
             obj.__tl_dict__ = threading.local().__dict__
 
-        result = obj.__tl_dict__[self.__name__] = self._func(obj)
-        return result
+        value = obj.__tl_dict__.get(self.__name__, _missing)
+        if value is _missing:
+            value = self._func(obj)
+            obj.__tl_dict__[self.__name__] = value
+        return value