On Monday, 5 March 2018 23:06:53 UTC, Steven D'Aprano wrote: > On Mon, 05 Mar 2018 09:22:33 -0800, Ooomzay wrote: > [...] > > If you would like to have a shot at coding this without RAII, but > > preserving the OO design, you will find that it is considerably > > simpler than the with/context manager approach. > > Preserving the OO design, you say? Okay, since my application apparently > isn't allowed to know that it is processing two files, I'll simply > delegate that to the object: > > class C(A, B): > def run(self): > with open(self.a) as a: > with open(self.b) as b: > process(a, b) > > # Later. > if __name__ = '__main__': > # Enter the Kingdom of Nouns. > c = C() > c.run() > > There you go. Encapsulation and OO design.
1. This does not execute. It is only when you actually flesh out these deliberately minimal classes A, B & C with PEP232 paraphernalia that we all be able to see clearly how much cleaner or messier things are with PEP232. 2. Your Class C breaks A & B's encapsulation by inheriting rather than composing them. Apart from increasing coupling and preventing substitution, C contained A & B in this example to illustrate that there is no RAII related burden whatever_on this intermediate class as it manages no external resources directly. It does not even need to implement __del__. 3. You have assumed a single threaded application. Please imagine that A and B are classes managing some remote valves and maintain their own threads as well as a serial port for comms. And C is there to coordinate them towards some greater purpose. If you would like to try and add PEP232 support to classes A,B & C to the point that you can create and destroy c = C() in an exception-safe way we may all learn something. > I'm not trying to dissuade you from using RAII in your own applications, > if it works for you, great. Unfortunately, despite having conquered it, without a _guarantee_ of this behaviour from the language, or at least one mainstream implementation, I will not invest in python again. Nor recommend any one else with a serious real world resource management application to do so. This was the original motive for my PEP. -- https://mail.python.org/mailman/listinfo/python-list
