Seems nice. Just write a library and upload it to one of the usual places?
On Thu, 31 Aug 2023, 16:54 Tim Hoffmann via Python-ideas, <
python-ideas@python.org> wrote:
> The standard pattern to create a sentinel in Python is
>
> >>> Unset = object()
>
> While this is often good enough, it has some shortcomings:
>
> - repr(Unset) is unhelpful: <object at 0x1ded9911b60>
>
> - copy/deepcopy create a copy of the sentinel object, which can lead to
> surprising results such as:
> >>> d = {'val': Unset}
> >>> d['val'] is Unset
> True
> >>> d2 = copy.deepcopy(d)
> >>> d2['val'] is Unset
> False
>
> - The code "Unset = object()" is quite obscure for people not familiar
> with the sentinel pattern.
>
>
> I propose to provide a sentinel() factory function so that
>
> >>> Unset = sentinel("Unset")
> >>> repr(unset)
> <Unset>
> >>> copy.copy(Unset) is Unset
> True
> >>> copy.deepcopy(Unset) is Unset
> True
>
>
> A simple implementation would be something like
>
> def sentinel(name):
> return type(name, (), {
> '__repr__': lambda self: f"<{self.__class__.__name__}>",
> '__copy__': lambda self: self,
> '__deepcopy__': lambda self, memo: self,
> })
>
> Likely, the implementation should be refined a bit more.
>
>
> While it's not rocket science, getting sentinels correct is cumbersome for
> end users. Providing such a function in the standard library is only a
> minor maintainance burden, but a significant help for users working with
> sentinels.
>
> Thanks for your consideration!
> Tim
> _______________________________________________
> Python-ideas mailing list -- python-ideas@python.org
> To unsubscribe send an email to python-ideas-le...@python.org
> https://mail.python.org/mailman3/lists/python-ideas.python.org/
> Message archived at
> https://mail.python.org/archives/list/python-ideas@python.org/message/BXTIVPVDHW644AX3EAJU36A2GFCPX3QS/
> Code of Conduct: http://python.org/psf/codeofconduct/
>
_______________________________________________
Python-ideas mailing list -- python-ideas@python.org
To unsubscribe send an email to python-ideas-le...@python.org
https://mail.python.org/mailman3/lists/python-ideas.python.org/
Message archived at
https://mail.python.org/archives/list/python-ideas@python.org/message/BMM3ARGWC3AJGPHNUP5IUHYEGHK57RIC/
Code of Conduct: http://python.org/psf/codeofconduct/
