gh-153896: Deduplicate unhashable Literal params by Maxinho96 · Pull Request #153914 · python/cpython · GitHub

Issue: Literal[...] deduplication silently skips when values are unhashable #153896

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#153913 was just open a few minutes ago, but maybe @sobolevn wants relinquish his right to the PR

Sure, since this is the first contribution by @Maxinho96, I would prefer to merge their PR :)

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⚽️ I am a huge ⚪️🔵 Lazio 🦅 fan

Oh no, closing! 😱
I am AS Roma fan 😱

I am joking, obviously (not about the Roma part) :)
Thanks for the PR! And welcome :)

We ususally want lines under 80 charactesr, so I suggest that you rename value_and_type_parameters to a shorter name or you use the same format as Nikita:

    parameters = tuple(
        p
        for p, _ in _deduplicate(
            list(_value_and_type_iter(parameters)),
            unhashable_fallback=True,
        )
    )

6e95e84

For the future: how do I enforce the correct formatting? The pre-commit hook passed for some reason. I see it uses ruff, but if I run it one the codebase it changes all the files

Unfortunately, this is a manual task =/ we do have some parts of the stdlib with ruff configs, but for historical reasons, we don't enforce style on old files (for maintenance and diff purposes) and only try to enforce them for new code (so code you add, or code you change around). See PEP-7/PEP-8 guidelines (while they are guidelines, sometimes we need to break them because it's not consistent).

What we aim for:

Minimal diff in general.
If possible PEP-7/PEP-8 style if this doesn't introduce too many unrelated changes.
If not psosible, keep consistent style.

@Maxinho96 Make sure to add a NEWS entry as well :)

Oh no, closing! 😱 I am AS Roma fan 😱

@sobolevn lol what are the chances? I forgive you for your sins since you kindly let me contribute, thanks! 🙏🏻

Thanks! This looks good to me.

I think backporting makes sense here. It's unlikely that people are relying on this in a way that would break code; if anything, people could have been running their own deduplication pass on __args__, but that won't be broken by this fix.

GH-153914) (#153956) gh-153896: Deduplicate unhashable arguments in `typing.Literal` (GH-153914) (cherry picked from commit a53b5b1) Co-authored-by: Massimiliano Bruni <massimiliano.bruni@icloud.com>

GH-153914) (#153957) gh-153896: Deduplicate unhashable arguments in `typing.Literal` (GH-153914) (cherry picked from commit a53b5b1) Co-authored-by: Massimiliano Bruni <massimiliano.bruni@icloud.com>

GH-153914) (#153955) gh-153896: Deduplicate unhashable arguments in `typing.Literal` (GH-153914) (cherry picked from commit a53b5b1) Co-authored-by: Massimiliano Bruni <massimiliano.bruni@icloud.com> Co-authored-by: Tomas R. <tomas.roun8@gmail.com>

python/cpython#153914 deduplicates unhashable arguments.

…l dedup test_literal_values_unhashable_type asserts that duplicate unhashable Literal values (e.g. Literal[[1, 'a'], [1, 'a']]) are preserved, but CPython 3.13.15+ deduplicates unhashable Literal args at construction time (python/cpython#153914). Upstream fixed this the same way starting in 0.4.4 by skipping the test on newer Python; backport that same guard here since this recipe is pinned to 0.4.2. AI-Generated: Uses Claude Code Signed-off-by: Khem Raj <raj.khem@gmail.com>

fix(typing): deduplicate unhashable Literal params

9bdf823

Maxinho96 requested review from AlexWaygood and JelleZijlstra as code owners July 18, 2026 10:38

bedevere-app Bot added the awaiting review label Jul 18, 2026

bedevere-app Bot mentioned this pull request Jul 18, 2026

Literal[...] deduplication silently skips when values are unhashable #153896

Closed

Maxinho96 mentioned this pull request Jul 18, 2026

gh-153896: Deduplicate mutable args in Literal type #153913

Closed

tests: add 2 more test cases

9442d6a

picnixz reviewed Jul 18, 2026

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tomasr8 added the sprint label Jul 18, 2026

github-project-automation Bot added this to Sprint Jul 18, 2026

github-project-automation Bot moved this to Todo in Sprint Jul 18, 2026

picnixz reviewed Jul 18, 2026

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Comment thread Lib/test/test_typing.py Outdated

📜🤖 Added by blurb_it.

6ec1018

Maxinho96 added 2 commits July 18, 2026 13:04

chore: mutable -> unhashable

80caf68

style: formatting

6e95e84

ZeroIntensity approved these changes Jul 18, 2026

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github-project-automation Bot moved this from Todo to In Progress in Sprint Jul 18, 2026

bedevere-app Bot added awaiting merge and removed awaiting review labels Jul 18, 2026

ZeroIntensity added needs backport to 3.13 bugs and security fixes needs backport to 3.14 bugs and security fixes needs backport to 3.15 pre-release feature fixes, bugs and security fixes labels Jul 18, 2026

bedevere-app Bot removed the needs backport to 3.13 bugs and security fixes label Jul 18, 2026

Viicos added a commit to pydantic/typing-inspection that referenced this pull request Aug 10, 2026

Fix Literal test (#56 )

f576d83

python/cpython#153914 deduplicates unhashable arguments.

AlexWaygood mentioned this pull request Aug 12, 2026

Remove obsolete Literal deduplication assertion python/typing_extensions#785

Merged

		value_and_type_parameters = list(_value_and_type_iter(parameters))
		deduplicated_parameters = tuple(p for p, _ in _deduplicate(value_and_type_parameters, unhashable_fallback=True))

gh-153896: Deduplicate unhashable Literal params by Maxinho96 · Pull Request #153914 · python/cpython · GitHub

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gh-153896: Deduplicate unhashable Literal params - #153914

gh-153896: Deduplicate unhashable Literal params#153914ZeroIntensity merged 5 commits intopython:mainpython/cpython:mainfrom Maxinho96:mainMaxinho96/cpython:mainCopy head branch name to clipboard

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gh-153896: Deduplicate unhashable Literal params#153914
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