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Title: Test identity first in membership operation of ItemsView, ValuesView and Sequence in
Type: behavior Stage: resolved
Components: Library (Lib) Versions: Python 3.6
Status: closed Resolution: fixed
Dependencies: Superseder:
Assigned To: Nosy List: josh.r, python-dev, rhettinger, serhiy.storchaka, stutzbach, xiang.zhang
Priority: normal Keywords: patch

Created on 2016-05-03 06:19 by xiang.zhang, last changed 2022-04-11 14:58 by admin. This issue is now closed.

File name Uploaded Description Edit
issue26915.patch xiang.zhang, 2016-05-03 06:20 review
issue26915_v2.patch xiang.zhang, 2016-05-03 06:24 review
issue26915_s2.patch xiang.zhang, 2016-05-05 10:29 review
issue26915_v3.patch xiang.zhang, 2016-06-04 08:33 review
issue26915_v4.patch xiang.zhang, 2016-06-04 08:42 review
Pull Requests
URL Status Linked Edit
PR 503 merged xiang.zhang, 2017-03-06 09:14
PR 553 merged xiang.zhang, 2017-03-08 03:16
PR 703 larry, 2017-03-17 21:00
Messages (19)
msg264688 - (view) Author: Xiang Zhang (xiang.zhang) * (Python committer) Date: 2016-05-03 06:19
__contains__ operation in ItemsView, ValuesView and Sequence in simply test equality with ==. This introduces inconsistent behaviour with built-in containers when encountering objects like NaN, which does not equal to itself. I asked something about this on core-mentorship, see
msg264689 - (view) Author: Xiang Zhang (xiang.zhang) * (Python committer) Date: 2016-05-03 06:24
Add issue number to test method name.
msg264764 - (view) Author: Josh Rosenberg (josh.r) * (Python triager) Date: 2016-05-03 20:30
At some point someone really needs to decide if the C layer behavior of performing an identity test before full equality checking is something that should be emulated at the Python layer or not. The current state seems ridiculous, where C containers check identity first simply by using the easier RichCompareBool function, while Python containers have to have the identity-then-equality check rewritten explicitly, which feels like a DRY violation.

Makes it harder for non-CPython implementations too, since they end up either not matching CPython behavior, or writing extra code to match the CPython quirks.

I have nothing against this patch, but between PyObject_RichCompareBool and the various slightly strange behaviors in the argument parsing format codes (which leads to silly workarounds like _check_int_field in #20858), I feel like the Python code base is getting cluttered with hacks to emulate the hacky C layer.
msg264773 - (view) Author: Xiang Zhang (xiang.zhang) * (Python committer) Date: 2016-05-04 02:34
I agree with you josh. Actually that's what I want to know, consistency. But I don't mention it in my post, so Guido only gives what to do in this case. In this thread, it means does Python code have to keep the invariant mentioned in msg75735?
msg264891 - (view) Author: Roundup Robot (python-dev) (Python triager) Date: 2016-05-05 08:14
New changeset 1c6cf4010df3 by Raymond Hettinger in branch 'default':
Issue 26915:  Add identity checks to the collections ABC __contains__ methods.
msg264892 - (view) Author: Raymond Hettinger (rhettinger) * (Python committer) Date: 2016-05-05 08:17
Xiang, hanks for the patch and for the link to Guido's opinion.

Josh, I concur with your sentiments.  In this case the burden is light and is likely to prevent future difficulties by keeping the container invariants intact.
msg264896 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2016-05-05 08:25
Is it worth to add a function in the operator module that tests arguments for identity or equality?
msg264898 - (view) Author: Xiang Zhang (xiang.zhang) * (Python committer) Date: 2016-05-05 08:50
In my opinion it's not worth. If there is such an operator in stdlib, I would expect more, exposing PyObject_RichCompareBool in Python level, providing a new operator like `===`.
msg264900 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2016-05-05 09:16
What about Sequence.index and Sequence.count?
msg264902 - (view) Author: Xiang Zhang (xiang.zhang) * (Python committer) Date: 2016-05-05 10:29
Oops, I forgot about them. I think they should. Raymond mentioned count in msg75735. Attach patch to take them in.
msg266151 - (view) Author: Xiang Zhang (xiang.zhang) * (Python committer) Date: 2016-05-23 14:13
Reopen this since the solution is not complete pointed out by Serhiy and the new patch has already been attached(s2).
msg267106 - (view) Author: Xiang Zhang (xiang.zhang) * (Python committer) Date: 2016-06-03 15:36
Serhiy, actually the patch(issue26915_s2.patch) I uploaded early has tried to make Sequence.index and Sequence.count consistent. Maybe the issue stage is not right.
msg267124 - (view) Author: Serhiy Storchaka (serhiy.storchaka) * (Python committer) Date: 2016-06-03 18:09
Oh, sorry, I was absentminded. In general the patch LGTM. But I think that using list subclass for tests is not a good idea. If we make a typo in CustomSequence method name (__contain__, inedx, coumt), the test is still passed. It would be better to use a class that doesn't have any sequence-related methods besides explicitly defined.
msg267247 - (view) Author: Xiang Zhang (xiang.zhang) * (Python committer) Date: 2016-06-04 08:33
Thanks for review Serhiy and nice thoughts. I make the class inherited directly from Sequence. So if the methods in Sequence are OK, the test class is OK.
msg267248 - (view) Author: Xiang Zhang (xiang.zhang) * (Python committer) Date: 2016-06-04 08:42
Oh, sorry. Make the __len__ signature wrong. Change it.
msg269877 - (view) Author: Xiang Zhang (xiang.zhang) * (Python committer) Date: 2016-07-06 10:12
msg271151 - (view) Author: Xiang Zhang (xiang.zhang) * (Python committer) Date: 2016-07-24 13:38
Ping again.
msg290275 - (view) Author: Xiang Zhang (xiang.zhang) * (Python committer) Date: 2017-03-24 22:43
New changeset 78ad039bcf1a8c494cbc8e18380cc30665869c3e by Xiang Zhang in branch '3.6':
bpo-26915: Test identity first in index() and count() of  (GH-553)
msg290277 - (view) Author: Xiang Zhang (xiang.zhang) * (Python committer) Date: 2017-03-24 22:43
New changeset d5d3249e8a37936d32266fa06ac20017307a1f70 by Xiang Zhang in branch 'master':
bpo-26915: Test identity first in membership operation in index() and count() methods of (GH-503)
Date User Action Args
2022-04-11 14:58:30adminsetgithub: 71102
2022-01-20 22:53:07iritkatriellinkissue23162 superseder
2017-03-24 22:43:22xiang.zhangsetmessages: + msg290277
2017-03-24 22:43:01xiang.zhangsetmessages: + msg290275
2017-03-17 21:00:35larrysetpull_requests: + pull_request609
2017-03-08 03:44:58xiang.zhangsetstatus: open -> closed
resolution: fixed
stage: patch review -> resolved
2017-03-08 03:16:07xiang.zhangsetpull_requests: + pull_request454
2017-03-06 09:14:04xiang.zhangsetpull_requests: + pull_request411
2016-07-24 13:38:52xiang.zhangsetmessages: + msg271151
2016-07-06 10:12:32xiang.zhangsetmessages: + msg269877
2016-06-04 08:42:28xiang.zhangsetfiles: + issue26915_v4.patch

messages: + msg267248
2016-06-04 08:33:20xiang.zhangsetfiles: + issue26915_v3.patch

messages: + msg267247
2016-06-03 18:09:43serhiy.storchakasetstage: needs patch -> patch review
2016-06-03 18:09:34serhiy.storchakasetmessages: + msg267124
2016-06-03 15:36:34xiang.zhangsetmessages: + msg267106
2016-06-03 12:09:32serhiy.storchakasetresolution: fixed -> (no value)
stage: patch review -> needs patch
2016-05-24 07:18:39rhettingersetassignee: rhettinger ->
2016-05-23 14:13:43xiang.zhangsetstatus: closed -> open

messages: + msg266151
2016-05-05 10:29:16xiang.zhangsetfiles: + issue26915_s2.patch

messages: + msg264902
2016-05-05 09:16:50serhiy.storchakasetmessages: + msg264900
2016-05-05 08:50:24xiang.zhangsetmessages: + msg264898
2016-05-05 08:25:07serhiy.storchakasetmessages: + msg264896
2016-05-05 08:17:31rhettingersetstatus: open -> closed
resolution: fixed
messages: + msg264892
2016-05-05 08:14:17python-devsetnosy: + python-dev
messages: + msg264891
2016-05-04 02:34:20xiang.zhangsetmessages: + msg264773
2016-05-03 20:48:39serhiy.storchakasetassignee: rhettinger

nosy: + serhiy.storchaka
2016-05-03 20:30:22josh.rsetnosy: + josh.r
messages: + msg264764
2016-05-03 06:24:36xiang.zhangsetfiles: + issue26915_v2.patch

messages: + msg264689
2016-05-03 06:23:53SilentGhostsetnosy: + rhettinger, stutzbach

type: behavior
stage: patch review
2016-05-03 06:20:37xiang.zhangsetfiles: + issue26915.patch
keywords: + patch
2016-05-03 06:19:16xiang.zhangcreate