On Tue, May 25, 2021 at 11:25 AM Pascal Chambon <python...@gmail.com> wrote:
>
> Hello, and thanks for the PEP,
>
> I feel like the 3-lines declaration of a new sentinel would discourage a
> bit its adoption compared to just "sentinel = object()"
I now tend to agree. The new version of the draft PEP proposes a
simpler interface: NotGiven = sentinel('NotGiven')
> From what I understand from the PEP, if new classes are defined inside
> the closure of a factory function, some Python implementations would
> have trouble copying/pickling them?
The reference implementations I propose take care of this. I'll make
sure that everything works in popular alternate implementations such
as PyPy.
> Would it be doable to have a single Sentinel class, whose instances
> store their representation and some autogenerated UUID, and which
> automatically return internally stored singletons (depending on this
> UUID) when called multiple times or unpickled ?
> This would require some __new__() and unpickling magic, but nothing too
> CPython-specific (or am I missing something?).
That's certainly doable, and I believe that there are existing
implementations of sentinels that use this method. But since classes
are singletons, and it's simple to make a class that always returns
the same object, there's no need for setting a UUID and implementing
custom pickling logic as you suggest.
Another drawback of this approach is that each sentinel value wouldn't
have its own dedicated type.
- Tal
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