Thanks for this, Luciano! My main issue with using class objects is that such use of them would be unusual and potentially confusing. I think that is important in general, and doubly so for something I suggest adding to the stdlib.
Additionally, I very much would like for each sentinel object to have its own dedicated class, to allow writing strict function type signatures. Once one adds that to a meta-class or class decorator, the complexity of the implementation approaches what I currently have for a sentinel() function. At that point, I can't see a clear advantage for such an approach. - Tal On Mon, May 24, 2021 at 7:31 PM Luciano Ramalho <luci...@ramalho.org> wrote: > On Mon, May 24, 2021 at 11:44 AM Tal Einat <talei...@gmail.com> wrote: > > > But frankly Luciano's idea of a base class that can be subclassed > seems the most startightford to me. > > > > Yes, and it's what I originally suggested near the beginning of this > thread :) > > I am sorry to have missed your previous e-mail with a base class for > sentinels, @Tal. I support that idea. > > In fact, if we have a SentinelMeta metaclass, and a Sentinel base > class built from SentinelMeta, the Sentinel class can be used directly > as a sentinel without the need for subclassing—if the application does > not require a custom sentinel. If it does, then the user can subclass > Sentinel. > > The SentinelMeta could be private, to discourage misuse. > > This is my implementation, after learning from @Tal's code: > > > https://github.com/fluentpython/example-code-2e/blob/master/25-class-metaprog/sentinel/sentinel.py > > Since having a Sentinel base class is desirable for ease of use, I > think it is simpler to code the __new__ method in it, instead of > coding metaclass logic to inject __new__ in the class namespace. > > Best, > > Luciano > > > > -- > Luciano Ramalho > | Author of Fluent Python (O'Reilly, 2015) > | http://shop.oreilly.com/product/0636920032519.do > | Technical Principal at ThoughtWorks > | Twitter: @ramalhoorg >
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