On Wednesday, March 15, 2017 at 11:33:56 AM UTC+1, Peter Otten wrote: > marco.naw...@colosso.nl wrote: > > > Dear All, > > > > Summary of the question: > > Is it generally safe to dynamically change an objects class; if not > > under which conditions can it be considered safe. > > > > Context: > > Given the code below, I have no direct control over Base and M1. M1 > > is a instantiated by 'calling' the read-only property of Base. > > I would like to transparently switch behaviour from M1 to M2. I have > > tried several things, but finally settled on the code below. Although > > it works really well, I am not sure whether I am about to shoot myself > > in the foot. In short, what I do is derive from Base, shadow the read-only > > property 'my_prop' so it returns M2 and finally replace an objects > > __class__ attribute with my derived class. > > > > Any thoughts or comments? > > Saying that something is "safe" is always problematic. I'd rather look for > ways to break the code and then decide if you can live with these potential > problems. I'll start with > > - If Base is reimplemented in C __class__ may become read-only > - my_prop may be accessed by Base methods and expect an M1 instance
Ok. These are valid points. The first is not a real concern to me at the moment. The whole purpose of Base is to provide a higher level interface to the underlying C/C++ code. The second is more interesting. I was aware of this and checked the source code of the library. I know an M1 instance is not directly used by Base. In addition, I expose the exact same interface in M2. Thanks for the feedback. Much appreciated! Marco -- https://mail.python.org/mailman/listinfo/python-list
