Here's our current proposal for docs. Is there anything you'd like to add? https://github.com/python/cpython/pull/18659/files
On Wed, Feb 26, 2020 at 8:12 AM David Mertz <me...@gnosis.cx> wrote: > I think the "if unset" behavior is well handled by collections.ChainMap. > But I do think that fact should be prominent in any documentation of the > new dict Union operator. > > On Wed, Feb 26, 2020, 11:06 AM Guido van Rossum <gu...@python.org> wrote: > >> On Wed, Feb 26, 2020 at 7:43 AM Claudio Jolowicz <cjolow...@gmail.com> >> wrote: >> >>> In my experience, the expression `value |= other` is a common idiom >>> across >>> programming languages to provide a default for `value` if it is "unset". >>> For a >>> container-type, I would expect this operation, informally spoken, to be >>> applied >>> element-wise. In other words, the resulting dict would have the union of >>> keys, >>> with values supplied from `other` only if keys are missing in `value`. >>> >>> This would allow users to provide defaults in a dictionary of settings, >>> like >>> this: >>> >>> settings |= defaults >>> >>> As this usage generalizes a (perceived) common idiom, I would expect >>> people to >>> get bitten by this. >>> >> >> Interesting. Can you point to specific examples of this? In what other >> languages have you seen this? (Not that it would make us change PEP 584, >> but if this appears common we could probably warn about it prominently in >> docs and tutorials.) >> >> The pattern I'm familiar with for applying defaults always starts with >> the defaults and then adds the local overrides, so the PEP 584 behavior >> fits perfectly. (Probably because in Python before PEP 584 the most common >> operation is dict.update(), which has the same semantics.) >> >> -- >> --Guido van Rossum (python.org/~guido) >> *Pronouns: he/him **(why is my pronoun here?)* >> <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/> >> _______________________________________________ >> Python-Dev mailing list -- python-dev@python.org >> To unsubscribe send an email to python-dev-le...@python.org >> https://mail.python.org/mailman3/lists/python-dev.python.org/ >> Message archived at >> https://mail.python.org/archives/list/python-dev@python.org/message/JHXN342STNGSPX3NRAEXRS6JOXH5BCNU/ >> Code of Conduct: http://python.org/psf/codeofconduct/ >> > -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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