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Mention Ellipsis pickling in the docs#103660

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hauntsaninja merged 4 commits into
python:mainfrom
sterliakov:docs/st-ellipsis-serializable
Aug 30, 2023
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Mention Ellipsis pickling in the docs#103660
hauntsaninja merged 4 commits into
python:mainfrom
sterliakov:docs/st-ellipsis-serializable

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@sterliakov

@sterliakov sterliakov commented Apr 21, 2023

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I literally came to docs to check if Ellipsis can be pickled and unpickled, but had to try it in REPL instead. This micro PR updates the documentation page to mention that Ellipsis is picklable. (no issue code, since this is a minor doc-only change)

Needs backport to all maintained versions, because this behaviour did not change (at least it's picklable in versions 3.7 to 3.12, I haven't checked earlier versions).

@bedevere-bot bedevere-bot added docs Documentation in the Doc dir skip news awaiting review labels Apr 21, 2023
@AA-Turner

AA-Turner commented Apr 21, 2023

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Is this covered by ‘classes accessible from the top level of a module’? For example, NotImplemented isn’t contained in this list. Perhaps the ‘special’ thing about Ellipsis is the relation to ...?

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@sterliakov

sterliakov commented Apr 21, 2023

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Oh, I'd rather add NotImplemented too, thanks for the reminder! Just checked, and it's picklable as well.

Neither Ellipsis nor NotImplemented are covered by "classes accessible from..." at least because they are not classes... These five builtin singletons (with None, True, and False) are special due to their nature. In fact ... and NotImplemented are covered by "instances of such classes whose the result of calling __getstate__() is picklable", but this finding requires treating them in slightly unusual way (Ellipsis is not "instance of type types.EllipsisType" from the developer point of view, but a builtin truthy literal singleton, and the same logic applies to NotImplemented - instance of types.NotImplementedType).

@AA-Turner

AA-Turner commented Apr 21, 2023

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Oh, I'd rather add NotImplemented too, thanks for the reminder!

Just added a review suggestion on that point.

Good points about classes vs singleton instances of the types!

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hauntsaninja
hauntsaninja reviewed Apr 24, 2023
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If we're documenting this behaviour, ideally we should make sure it's tested as well.

@sterliakov

sterliakov commented Aug 29, 2023

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Sorry for having abandoned this PR for a while. All these cases (both NotImplemented and Ellipsis) are already covered by tests introduced in BPO6477 9 years ago together with None pickling test.

cpython/Lib/test/pickletester.py

Lines 1976 to 1983 in d08d49d

def test_singleton_types(self):
# Issue #6477: Test that types of built-in singletons can be pickled.
singletons = [None, ..., NotImplemented]
for singleton in singletons:
for proto in protocols:
s = self.dumps(type(singleton), proto)
u = self.loads(s)
self.assertIs(type(singleton), u)

@hauntsaninja hauntsaninja added the needs backport to 3.12 only security fixes label Aug 30, 2023
@hauntsaninja hauntsaninja enabled auto-merge (squash) August 30, 2023 00:44
@AA-Turner

AA-Turner commented Aug 30, 2023

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@hauntsaninja I've merged HEAD as the branch was out-of-date, so the checks would never succeed (& hence auto-merge would never happen)

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@hauntsaninja hauntsaninja merged commit 14ec0bb into python:main Aug 30, 2023
@miss-islington

miss-islington commented Aug 30, 2023

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Thanks @sterliakov for the PR, and @hauntsaninja for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11, 3.12.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

@bedevere-bot

bedevere-bot commented Aug 30, 2023

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GH-108661 is a backport of this pull request to the 3.12 branch.

@bedevere-bot bedevere-bot removed the needs backport to 3.12 only security fixes label Aug 30, 2023
miss-islington pushed a commit to miss-islington/cpython that referenced this pull request Aug 30, 2023
@sterliakov @miss-islington
Mention Ellipsis pickling in the docs (pythonGH-103660) …
d21ca65 
(cherry picked from commit 14ec0bb)

Co-authored-by: sterliakov <50529348+sterliakov@users.noreply.github.com>
@bedevere-bot

bedevere-bot commented Aug 30, 2023

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GH-108662 is a backport of this pull request to the 3.11 branch.

@bedevere-bot bedevere-bot removed the needs backport to 3.11 only security fixes label Aug 30, 2023
miss-islington pushed a commit to miss-islington/cpython that referenced this pull request Aug 30, 2023
@sterliakov @miss-islington
Mention Ellipsis pickling in the docs (pythonGH-103660) …
a9366f9 
(cherry picked from commit 14ec0bb)

Co-authored-by: sterliakov <50529348+sterliakov@users.noreply.github.com>
hauntsaninja pushed a commit that referenced this pull request Aug 30, 2023
@miss-islington @sterliakov
[3.11] Mention Ellipsis pickling in the docs (GH-103660) (#108662) …
a2c05a4 
Mention Ellipsis pickling in the docs (GH-103660)
(cherry picked from commit 14ec0bb)

Co-authored-by: sterliakov <50529348+sterliakov@users.noreply.github.com>
Yhg1s pushed a commit that referenced this pull request Aug 30, 2023
@miss-islington @sterliakov
[3.12] Mention Ellipsis pickling in the docs (GH-103660) (#108661) …
1d6d05a 
Mention Ellipsis pickling in the docs (GH-103660)
(cherry picked from commit 14ec0bb)

Co-authored-by: sterliakov <50529348+sterliakov@users.noreply.github.com>
carljm added a commit to carljm/cpython that referenced this pull request Aug 30, 2023
@carljm
Merge branch 'main' into icompexc …
37377e6 
* main:
  pythongh-108520: Fix bad fork detection in nested multiprocessing use case (python#108568)
  pythongh-108590: Revert pythongh-108657 (commit 400a1ce) (python#108686)
  pythongh-108494: Argument Clinic: Document how to generate code that uses the limited C API (python#108584)
  Document Python build requirements (python#108646)
  pythongh-101100: Fix Sphinx warnings in the Logging Cookbook (python#108678)
  Fix typo in multiprocessing docs (python#108666)
  pythongh-108669: unittest: Fix documentation for TestResult.collectedDurations (python#108670)
  pythongh-108590: Fix sqlite3.iterdump for invalid Unicode in TEXT columns (python#108657)
  Revert "pythongh-103224: Use the realpath of the Python executable in `test_venv` (pythonGH-103243)" (pythonGH-108667)
  pythongh-106320: Remove private _Py_ForgetReference() (python#108664)
  Mention Ellipsis pickling in the docs (python#103660)
  Revert "Use non alternate name for Kyiv (pythonGH-108533)" (pythonGH-108649)
  pythongh-108278: Deprecate passing the first param of sqlite3.Connection callback APIs by keyword (python#108632)
  pythongh-108455: peg_generator: install two stubs packages before running mypy (python#108637)
  pythongh-107801: Improve the accuracy of io.IOBase.seek docs (python#108268)
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