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Improve islice_extended memory usage when stop<0 and step>0#999

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bbayles merged 2 commits intomore-itertools:masterfrom
ben42code:u/ben42code/islice_extended_memory_usage2
Jun 27, 2025
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Improve islice_extended memory usage when stop<0 and step>0#999
bbayles merged 2 commits intomore-itertools:masterfrom
ben42code:u/ben42code/islice_extended_memory_usage2

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@ben42code ben42code commented Jun 7, 2025 •
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Issue reference

#1011
Follow up on issue #994

Scope

Improve islice_extended memory usage when stop<0 and step>0

This pull request cover the case when stop<0 and step>0 where we're currently holding a reference on that returned element one iteration step too long, since we store the yielded element in a temporary variable.

start<0 and step>0 was covered with #995 (improvement) and #996 (unit test)

Changes

  • Release the iterated element as soon as it's been returned, for islice_extended when stop<0 and step>0.
  • Update unit test to reflect/confirm lifecycle management improvement.

image

Checks and tests

On python 3.13

ruff format .
12 files left unchanged

python -m unittest -v 'tests.test_more.IsliceExtendedTests'
test_all (tests.test_more.IsliceExtendedTests.test_all) ... ok
test_elements_lifecycle (tests.test_more.IsliceExtendedTests.test_elements_lifecycle) ... ok
test_invalid_slice (tests.test_more.IsliceExtendedTests.test_invalid_slice) ... ok
test_slicing (tests.test_more.IsliceExtendedTests.test_slicing) ... ok
test_slicing_extensive (tests.test_more.IsliceExtendedTests.test_slicing_extensive) ... ok
test_zero_step (tests.test_more.IsliceExtendedTests.test_zero_step) ... ok

coverage report --show-missing --fail-under=99
Name                         Stmts   Miss  Cover   Missing
----------------------------------------------------------
more_itertools\__init__.py       3      0   100%
more_itertools\more.py        1612      1    99%   3411
more_itertools\recipes.py      354     16    95%   95-96, 104-105, 344-345, 994-1012, 1066
----------------------------------------------------------
TOTAL                         1969     17    99%

@ben42code
Improve islice_extended memory usage when stop<0 and step>0
a16e9c1 
Ensure we release iterated elements asap when stop<0 and step>0.
We're currently holding a reference on that last returned element one
iteration step too long, since we use a variable to hold the yielded element.

- Improved _islice_helper for start>0,stop<0,step>0.
- Updated unit test test_elements_lifecycle with improvement.
@ben42code ben42code force-pushed the u/ben42code/islice_extended_memory_usage2 branch from eab2b81 to addb37f Compare June 7, 2025 20:15
@ben42code
Remove obsolete comments on potential improvement
1a789ff 
- improvement has been introduced in previous commit.
- removing comments in a separate commit just for diff readability.
@ben42code ben42code force-pushed the u/ben42code/islice_extended_memory_usage2 branch from addb37f to 1a789ff Compare June 7, 2025 20:16
@ben42code ben42code mentioned this pull request Jun 20, 2025
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@ben42code
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ben42code commented Jun 20, 2025

Addresses following issue:

@ben42code ben42code mentioned this pull request Jun 21, 2025
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@ben42code ben42code changed the title U/ben42code/islice extended memory usage2 Improve islice_extended memory usage when stop<0 and step>0 Jun 21, 2025
@bbayles bbayles merged commit cea037c into more-itertools:master Jun 27, 2025
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@ben42code ben42code mentioned this pull request Jun 28, 2025
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2 participants

@ben42code @bbayles