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gh-153896: Deduplicate unhashable Literal params #153914

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Merged
ZeroIntensity merged 5 commits into from
Jul 18, 2026
+18 −8
Merged

gh-153896: Deduplicate unhashable Literal params #153914

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9bdf823
fix(typing): deduplicate unhashable Literal params
Maxinho96 Jul 18, 2026
9442d6a
tests: add 2 more test cases
Maxinho96 Jul 18, 2026
6ec1018
📜🤖 Added by blurb_it.
blurb-it[bot] Jul 18, 2026
80caf68
chore: mutable -> unhashable
Maxinho96 Jul 18, 2026
6e95e84
style: formatting
Maxinho96 Jul 18, 2026
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10 changes: 8 additions & 2 deletions Lib/test/test_typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2801,8 +2801,14 @@ def test_args(self):
self.assertEqual(Literal[1, 2, 3].__args__, (1, 2, 3))
self.assertEqual(Literal[1, 2, 3, 3].__args__, (1, 2, 3))
self.assertEqual(Literal[1, Literal[2], Literal[3, 4]].__args__, (1, 2, 3, 4))
# Mutable arguments will not be deduplicated
self.assertEqual(Literal[[], []].__args__, ([], []))
# Unhashable arguments will be deduplicated too
self.assertEqual(Literal[[], []].__args__, ([],))
self.assertEqual(Literal[{"a": 1}, {"a": 1}].__args__, ({"a": 1},))
self.assertEqual(
Literal[1, {'a': 'b'}, 2, {'a': 'b'}, 3].__args__,
(1, {'a': 'b'}, 2, 3),
)
self.assertEqual(Literal[{1}, {1}, {2}, {2}].__args__, ({1}, {2}))

def test_flatten(self):
l1 = Literal[Literal[1], Literal[2], Literal[3]]
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15 changes: 9 additions & 6 deletions Lib/typing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -775,13 +775,16 @@ def open_helper(file: str, mode: MODE) -> str:
# There is no '_type_check' call because arguments to Literal[...] are
# values, not types.
parameters = _flatten_literal_params(parameters)
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,
)
)

Comment on lines +778 to 786

@picnixz picnixz Jul 18, 2026

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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,
        )
    )

@Maxinho96 Maxinho96 Jul 18, 2026

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6e95e84

@Maxinho96 Maxinho96 Jul 18, 2026

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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

@picnixz picnixz Jul 18, 2026

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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.

try:
parameters = tuple(p for p, _ in _deduplicate(list(_value_and_type_iter(parameters))))
except TypeError: # unhashable parameters
pass

return _LiteralGenericAlias(self, parameters)
return _LiteralGenericAlias(self, deduplicated_parameters)


@_SpecialForm
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2026-07-18-10-52-10.gh-issue-153896.87oevp.rst
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@@ -0,0 +1 @@
Deduplicate unhashable args in :data:`typing.Literal`.
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