Message 362774 - Python tracker

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Author	gvanrossum
Recipients	Aaron Hall, brandtbucher, gvanrossum, josh.r, mark.dickinson, rhettinger, scoder, serhiy.storchaka, slam, steve.dower, xtreak
Date	2020-02-27.05:59:40
SpamBayes Score	-1.0
Marked as misclassified	Yes
Message-id	<1582783181.04.0.040346704677.issue36144@roundup.psfhosted.org>
In-reply-to

Content
I think for `\|=` the only choice is for it to be essentially an alias to `.update()`. So that means `cm \|= other` becomes `cm.maps[0].update(other)`. For `\|` we are breaking new ground and we could indeed make `cm \| other` do something like `ChainMap(other, cm.maps)`. I've not used ChainMap much (though I've seen some code that uses it) so I'm probably not the best judge of whether this is a good feature to have. Note that `other \| cm` will just do whatever `other.__or__` does, since ChainMap isn't a true subclass of dict, so it will not fall back to `cm.__ror__`. Basically ChainMap will not get control in this case. Other thoughts: - Maybe `cm1 \| cm2` (both ChainMaps) ought to return `ChainMap(cm2.maps, *cm1.maps)`? - These semantics make `\|=` behave rather differently from `\|`. Is that okay? If not, which of them should change, and how?

I think for `|=` the only choice is for it to be essentially an alias to `.update()`. So that means `cm |= other` becomes `cm.maps[0].update(other)`.

For `|` we are breaking new ground and we could indeed make `cm | other` do something like `ChainMap(other, *cm.maps)`.

I've not used ChainMap much (though I've seen some code that uses it) so I'm probably not the best judge of whether this is a good feature to have.

Note that `other | cm` will just do whatever `other.__or__` does, since ChainMap isn't a true subclass of dict, so it will not fall back to `cm.__ror__`. Basically ChainMap will not get control in this case.

Other thoughts:

- Maybe `cm1 | cm2` (both ChainMaps) ought to return `ChainMap(*cm2.maps, *cm1.maps)`?

- These semantics make `|=` behave rather differently from `|`. Is that okay? If not, which of them should change, and how?

History
Date	User	Action	Args
2020-02-27 05:59:41	gvanrossum	set	recipients: + gvanrossum, rhettinger, mark.dickinson, scoder, serhiy.storchaka, steve.dower, josh.r, Aaron Hall, slam, xtreak, brandtbucher
2020-02-27 05:59:41	gvanrossum	set	messageid: <1582783181.04.0.040346704677.issue36144@roundup.psfhosted.org>
2020-02-27 05:59:41	gvanrossum	link	issue36144 messages
2020-02-27 05:59:40	gvanrossum	create