On Sun, May 23, 2021 at 3:37 AM Tal Einat <talei...@gmail.com> wrote:
> I put up an early draft of a PEP on a branch in the PEPs repo:
> https://github.com/python/peps/blob/sentinels/pep-9999.rst
Thanks for that PEP, Tal. Good ideas and recap there.
I think repr= should have a default: the name of the class within <>:
<NotGiven>.
Sentinels don't have state or any other data besides a name, so I
would prefer not to force users to create a class just so they can
instantiate it.
Why not just this?
NotGiven = sentinel('<NotGiven>')
In this case it's harder to provide a good default repr.
On the other hand, if the user must create a class, the class itself
should be the sentinel. Class objects are already singletons, so that
makes sense.
Here is a possible class-based API:
class NotGiven(Sentinel):
pass
That's it. Now I can use NotGiven as the sentinel, and its default
repr is <NotGiven>.
Behind the scenes we can have a SentinelMeta metaclass with all the
magic that could be required--including the default __repr__ method.
What do you think?
Cheers,
Luciano
>
> (Note: This link will break once the temporary branch is deleted.)
>
> I wrote it to summarize the discussions, organize my thoughts and
> explore the options. I stopped working on it late at night and sent a
> link to a few people to get some opinions. I didn’t intend to make it
> public yet, but it was noticed and replied to on the
> discuss.python.org thread where I put up the poll [1], so the cat is
> out of the proverbial bag now…
>
> Luciano, your wish is granted! ;)
> - Tal Einat
>
> [1] https://discuss.python.org/t/sentinel-values-in-the-stdlib/8810/
--
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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