在django.utils.functional 里发现的。

  class cached_property(object):
      """
      Decorator that creates converts a method with a single
      self argument into a property cached on the instance.
      """
      def __init__(self, func):
          self.func = func

      def __get__(self, instance, type):
          res = instance.__dict__[self.func.__name__] = self.func(instance)
          return res

这玩意好用啊，比如

  >>> class A(object):
  ...   @cached_property
  ...   def val(self):
  ...     print 'calc'
  ...     return 1
  ... 
  >>> 
  >>> a=A()
  >>> a.val
  calc
  1
  >>> a.val
  1

以前自己山寨个 def val(): self._val = 什么的太烂了。