monkeypatching - dynamically set an instance property / memoized attribute in python? -

The current example class in my Python 2.7x

  class example (object): A = None B = Any C = None   
 And an existing example  
  An example = example () anInstance.a = 100 anInstance. B = 200 one ins. C = 300   
 I am reconstituting / cleaning some code, and now it is known that  anInstance.c  is an expensive operation Which is rarely used. / P> 
 In an ideal world I will do this:  
  class example (object): _c = none @property def c (self): if self._c is none: self ._c = Spend heavy duty here yourself C   
 The problem is that I can not change the  class example  right now. [Therefore, Quickfix will have to set it as a function, and I will replace every  obj.c  to  obj.c () ]  
 I know that there is no way, unless I can change the object, I can dynamically allocate a property / memoisonation. Is this understanding correct? I am hoping to be disappointed here, I just want confirmation.   
 
 
 You can change python classes Fact:  
  @property Def c (self): If self._c is not any: self._c = Heavy duty here to spend yourself here. C example example = c example._c = none   
 Now you've added an asset to your class  c , as well as  _c  attribute.  
 You may need to override any existing methods in the class, which they can assign to  self.c .  
 The process of dynamically adding or changing the properties of objects is often referred to as.