Provide a strict form of zip (PEP-618) requiring same length inputs

[gpshead]

BPO	40636
Nosy	@gvanrossum, @gpshead, @pitrou, @cool-RR, @serhiy-storchaka, @miss-islington, @brandtbucher
PRs	bpo-40636: Clarify the zip built-in docstring. #20118 [3.8] bpo-40636: Clarify the zip built-in docstring. (GH-20118) #20124 bpo-40636: PEP 618 implementation #20921 bpo-40636: Documentation for zip-strict #20961 bpo-40636: Remove overly-strict zip pickling tests #24109

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/brandtbucher'
closed_at = <Date 2020-06-24.17:15:46.811>
created_at = <Date 2020-05-15.19:25:39.377>
labels = ['interpreter-core', 'type-feature', '3.10']
title = 'Provide a strict form of zip (PEP-618) requiring same length inputs'
updated_at = <Date 2021-01-05.07:05:37.565>
user = 'https://github.com/gpshead'

bugs.python.org fields:

activity = <Date 2021-01-05.07:05:37.565>
actor = 'brandtbucher'
assignee = 'brandtbucher'
closed = True
closed_date = <Date 2020-06-24.17:15:46.811>
closer = 'brandtbucher'
components = ['Interpreter Core']
creation = <Date 2020-05-15.19:25:39.377>
creator = 'gregory.p.smith'
dependencies = []
files = []
hgrepos = []
issue_num = 40636
keywords = ['patch']
message_count = 13.0
messages = ['368965', '368977', '368980', '371870', '371899', '372272', '372300', '384239', '384243', '384310', '384338', '384339', '384370']
nosy_count = 8.0
nosy_names = ['gvanrossum', 'gregory.p.smith', 'pitrou', 'SilentGhost', 'cool-RR', 'serhiy.storchaka', 'miss-islington', 'brandtbucher']
pr_nums = ['20118', '20124', '20921', '20961', '24109']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue40636'
versions = ['Python 3.10']

[gpshead]

PEP-618 https://www.python.org/dev/peps/pep-0618 discussions are still on going. This issue is being filed to track an implementation, assuming the PEP is accepted and one is decided upon.

I'm filing it now, as I can at least use the issue for documentation enhancements of the existing zip() behavior.

[gpshead]

New changeset 6a5d3ff by Gregory P. Smith in branch 'master':
bpo-40636: Clarify the zip built-in docstring. (GH-20118)
6a5d3ff

[miss-islington]

New changeset c3d025a by Miss Islington (bot) in branch '3.8':
bpo-40636: Clarify the zip built-in docstring. (GH-20118)
c3d025a

[vstinner]

New changeset 310f6aa by Guido van Rossum in branch 'master':
bpo-40636: PEP-618: add strict parameter to zip() (GH-20921)
310f6aa

[gvanrossum]

New changeset 59cf853 by Ram Rachum in branch 'master':
bpo-40636: Documentation for zip-strict (bpo-20961)
59cf853

[SilentGhost]

Ram, please fix the typo pointed out on github 59cf853#r40044022

[cool-RR]

I'll fix that typo.

[serhiy-storchaka]

Tests test_zip_pickle_stability and test_zip_pickle_strict_stability look excessively strict. Why did we need them if there are other pickle tests? They prevent implementing optimizations like in bpo-36694.

[gvanrossum]

That's fair. How do other builtins validate their pickling implementation?

Since the pickling goes through __reduce__/reduce_ex we could instead test that those methods return the expected results, that pickling roundtrips, and that unpickling those exact byte strings produces the expected value?

[serhiy-storchaka]

For other types we do not have such strict tests. We just test that pickling roundtrips (it is already tested for zip() in other tests). There are few tests that unpickling some exact byte strings produces the expected value, but these tests are in pickletester.py, because they test the unpickling machinery. If unpickling of some type depends on some private constructor (like re._compile), that constructor can be tested separately.

So I think that these tests can be removed.

[gvanrossum]

Sounds good, go for it. I assume @brandtbucher won't mind.

[brandtbucher]

Yep, fine by me. I can remove them later today (unless Serhiy beats me to it).

[brandtbucher]

New changeset 27f9daf by Brandt Bucher in branch 'master':
bpo-40636: Remove overly-strict zip pickling tests (GH-24109)
27f9daf