On Mon, May 24, 2021 at 11:44 AM Tal Einat <taleinat@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-metapro... 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