[issue12445] dict view values objects are missing tp_richcmp and tp_as_number

[Peter Lovett]

Change by Peter Lovett :


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nosy: +PeterL777

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[issue12445] dict view values objects are missing tp_richcmp and tp_as_number

[Inada Naoki]

Inada Naoki  added the comment:

I don't think we need it.  So I reject it.

If you believe many Pythonista really need it,
please start discussion on python-dev.

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[issue12445] dict view values objects are missing tp_richcmp and tp_as_number

[Julian Berman]

Julian Berman  added the comment:

Yes I know *why* it worked in Py2 -- still seems like an oversight :)

To me, comparing (multi)set-like is the only reasonable behavior there
which is what IIRC the patch did, but even without that, for a given dict,
d.values() != d.values().

So, it's not like comparison is currently unimplemented. It returns
answers, they just mostly make no sense. (And of course I know that what's
happening is we're falling back to an identity check)

On Thu, Mar 28, 2019, 09:51 Inada Naoki  wrote:

>
> Inada Naoki  added the comment:
>
> > Well, surely there are reasonable semantics :), because dict.values ==
> > dict.values was comparable before we had view objects.
>
> Because it was list.
>
> Now values view is not sequence-like or set-like.
>
> >>> {"a": "foo", "b": "bar"}.values() == {"a": "bar", "b": "foo"}.value()
> True if set-like.  False if sequence-like.
>
> If you want Python 2 behavior, you should convert it to list.
> Then you can use "sequence" semantics.
>
> --
>
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[issue12445] dict view values objects are missing tp_richcmp and tp_as_number

[Inada Naoki]

Inada Naoki  added the comment:

> Well, surely there are reasonable semantics :), because dict.values ==
> dict.values was comparable before we had view objects.

Because it was list.

Now values view is not sequence-like or set-like.

>>> {"a": "foo", "b": "bar"}.values() == {"a": "bar", "b": "foo"}.value()
True if set-like.  False if sequence-like.

If you want Python 2 behavior, you should convert it to list.
Then you can use "sequence" semantics.

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[issue12445] dict view values objects are missing tp_richcmp and tp_as_number

[Julian Berman]

Julian Berman  added the comment:

Well, surely there are reasonable semantics :), because dict.values ==
dict.values was comparable before we had view objects.

It's been awhile since I filed this, and still seems rather silly that:

 {"a": "foo"}.values() != {"a": "foo"}.values()
True

On Thu, Mar 28, 2019 at 9:18 AM Inada Naoki  wrote:

>
> Inada Naoki  added the comment:
>
> There is no reasonable semantics for values view.
> Keep it unimplemented.
>
> --
> nosy: +inada.naoki
> resolution:  -> rejected
> stage: patch review -> resolved
> status: open -> closed
>
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[issue12445] dict view values objects are missing tp_richcmp and tp_as_number

[Inada Naoki]

Inada Naoki  added the comment:

There is no reasonable semantics for values view.
Keep it unimplemented.

--
nosy: +inada.naoki
resolution:  -> rejected
stage: patch review -> resolved
status: open -> closed

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[issue12445] dict view values objects are missing tp_richcmp and tp_as_number

[Julian]

Julian  added the comment:

Looking over this again with a clear head, adding the number operators is the 
incorrect thing to do here I think, since that function was also written 
assuming we had a set-like view object as input.

I am inclined to think that the correct behavior here for those operators is to 
not change that function, but to not make values objects add-able at all, even 
with other values objects, which would probably be the only other logical 
choice,  so leaving that as it was before (but still making the equality 
change).

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[issue12445] dict view values objects are missing tp_richcmp and tp_as_number

[Ezio Melotti]

Changes by Ezio Melotti :


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nosy: +ezio.melotti, rhettinger
stage:  -> patch review

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[issue12445] dict view values objects are missing tp_richcmp and tp_as_number

[Julian]

New submission from Julian :

dict view values() objects are missing tp_richcmp and tp_as_sequence, and the 
tests for those were incomplete, which means that on 2.7 and 3.2 (and on 
current head) viewvalues / values objects don't compare correctly. Without 
indication, I assume this is not the desired behavior.

Looks like the cause is that the dictview_richcompare function was written to 
expect a set-like object, and nothing was written for values. I've modified it 
to accept any view object and do the appropriate check.

One thing I'm unsure of, which I'm sure one of you will help with, is what the 
desired behavior is on what values() view objects actually *should* be equal 
to. Being that there isn't a multiset object, and that I couldn't find any 
resource, I assumed that they only should be equal to other values() objects, 
not any of the other (ordered) containers. If that's incorrect, or if I need to 
discuss that on the mailing list, please let me know.

A patch to fix both is attached with the correction to the unit test, hope I 
did this correctly. I assume this needs to be backported to 2.7, but I figured 
I'd ask about that first. (Test suite runs without errors on current 3.3 head 
with this patch for me).

dictview_richcompare also needs unit tests for the NotImplemented error that it 
should return, but I didn't want to convolute this patch, please let me know if 
I should put that in here, or file another ticket, or neither.

Thanks!

--
components: Interpreter Core
files: viewvalues_compare.patch
keywords: patch
messages: 139455
nosy: Julian
priority: normal
severity: normal
status: open
title: dict view values objects are missing tp_richcmp and tp_as_number
type: behavior
versions: Python 2.7, Python 3.2, Python 3.3
Added file: http://bugs.python.org/file22518/viewvalues_compare.patch

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