On 10/29/2012 12:05 PM, andrea crotti wrote: > I meant how do I create new immutables classes myself, I guess that's > possible writing C extensions but I don't see in pure Python..
The short answer is: you don't, not really, except by using NamedTuple if that gives you what you want. The longer answer: You can kinda get it somewhat if you define your own __getattribute__/__setattribute__ functions. __setattribute__ of course should never do anything except raise an error (one way or another you'll need to make an exception for your __init__ function of course). __getattribute__ should make sure no mutable references are returned: e.g. you'll probably want to make it so someone can't side-step your setter by saying someobject.__dict__["foo"] = "bar". (I return a copy of the dict.) It will still be possible to bypass these protections though. To really get true immutability in pure Python, you'll have to inherit from tuple or NamedTuple (which inherits from tuple, I think). You can see some discussion on Stack Overflow and some other places about this; having played around with this a bit, I think it's not worth the hassle and have done the __getattribute__/__setattribute__ thing the couple of times I wanted immutability. Evan
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