There's an implementation of a sentinel object in unittest.mock : >>> from unittest.mock import sentinel >>> sentinel.THING sentinel.THING
On Thu, 8 Jun 2023 at 15:20, David Mertz, Ph.D. <david.me...@gmail.com> wrote: > https://peps.python.org/pep-0661/ > > On Thu, Jun 8, 2023 at 9:58 AM Dom Grigonis <dom.grigo...@gmail.com> > wrote: > >> This has been bugging me for a long time. It seems that python doesn’t >> have a convention for “Undefined” type. >> >> When I started using python I naturally used None for it (as advised). >> >> However, the more I work with python, the more I find that None is a >> meaningful type. And it is a type that is convenient to use in a lot of >> cases, where it is not actually “None”. >> >> One big example is: >> numpy: array[None, :] >> >> Another is simple cascading of defaults. >> E.g. >> >> ```python >> class A: >> def __init__(self, default=’string'): >> self.default = default >> >> def method(self, default=None): >> default = default if default is not None else self.default >> dct[‘key’] = other_dict.get(‘key’, default) >> return to_json(dct) >> ``` >> >> None has a logic in `some_func`, which is important. >> Now if I want to enforce None passed to to_json I have no way to do it. >> >> I know there are many workarounds for this, but there is no `consistent` >> way of doing this. >> >> I have been using Ellipsis in the past, but it doesn’t feel right, >> because it also has a meaning and I might need to use those functions with >> e.g. numpy in he future and will have to change it. >> >> Now, I came back to this issue again and my latest solution is to just >> define: >> UNDEFINED = object() >> in library constants.py >> >> Then code above is very clear and I think this is a good and sustainable >> solution. >> >> I know, that in a way ’None’ is already this, but it is generally used in >> 2 ways: >> 1. A variable/argument is undefined in python space >> 2. Global indication, that a value is undefined (e.g. equivalence of null >> in json) >> >> What I am proposing is to have 1 more constant in python ‘Undefined’, >> which will indicate ‘Undefined’ in python space and leave None to be used >> in more general sense. >> >> I also found this article while looking for solution just now: >> >> https://levelup.gitconnected.com/python-why-none-is-not-nothing-bb3de55dd471 >> It seems that people who use typing are also running into ambiguities and >> trying to hack something together. >> I avoid typing until its 99% mature so can't comment more on this. >> >> What are your thoughts? Am I onto something or am I missing something? >> Anyone else had similar encounters? >> >> >> >> >> >> >> >> >> _______________________________________________ >> 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/RGUNJYXWHE7UM2W6FCAMGLJVLXEYHA2Q/ >> Code of Conduct: http://python.org/psf/codeofconduct/ >> > > > -- > The dead increasingly dominate and strangle both the living and the > not-yet born. Vampiric capital and undead corporate persons abuse > the lives and control the thoughts of homo faber. Ideas, once born, > become abortifacients against new conceptions. > _______________________________________________ > 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/YTCPDFDUZTMTXS5LYHKCYJ23WVMPE6CL/ > Code of Conduct: http://python.org/psf/codeofconduct/ > -- Michael Foord Python Consultant, Contractor and Trainer https://agileabstractions.com/
_______________________________________________ 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/YNKTVZM6GMQAGR5XAJ3SH6HTAWGYG5VT/ Code of Conduct: http://python.org/psf/codeofconduct/
