8000 Add support for literal addition by cdce8p · Pull Request #18004 · python/mypy · GitHub
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Add support for literal addition #18004

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Add support for literal addition #18004

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3ef962d
Add support for literal addition
cdce8p Oct 20, 2024
0024062
Only infer LiteralType if one of thhe operands is a Literal
cdce8p Oct 21, 2024
9ead9fb
Fix tests
cdce8p Oct 21, 2024
c0c0a3f
Minor improvements
cdce8p Oct 22, 2024
12b518e
Move accept call to caller
cdce8p Nov 20, 2024
d14b697
Add additional test cases
cdce8p Nov 20, 2024
bc65724
Add guard against too many literal values
cdce8p Dec 9, 2024
c22d563
Remove type ignore
cdce8p May 19, 2025
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Add guard against too many literal values
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@cdce8p
cdce8p committed May 19, 2025
commit bc657245acb54653b56e333dc0d38cf79ad5591e
6 changes: 6 additions & 0 deletions mypy/checkexpr.py
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Original file line number Diff line number Diff line change
Expand Up @@ -212,6 +212,10 @@
# see https://github.com/python/mypy/pull/5255#discussion_r196896335 for discussion.
MAX_UNIONS: Final = 5

# Use fallback type if literal addition of unions results in too many literal
# values. Explicitly set on the safe side to prevent accidental issues.
MAX_LITERAL_ADDITION_VALUES: Final = 15


# Types considered safe for comparisons with --strict-equality due to known behaviour of __eq__.
# NOTE: All these types are subtypes of AbstractSet.
Expand Down Expand Up @@ -3635,6 +3639,8 @@ def literal_expression_addition(
)
if len(values) == 1:
return LiteralType(values[0], self.named_type(lvalue[1]))
elif len(values) > MAX_LITERAL_ADDITION_VALUES:
return None
return make_simplified_union(
[LiteralType(val, self.named_type(lvalue[1])) for val in values]
)
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9 changes: 9 additions & 0 deletions test-data/unit/check-literal.test
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Expand Up @@ -3089,3 +3089,12 @@ def func(d: LookupDict, pos: Literal["top_", "bottom_", ""]) -> str:

[builtins fixtures/dict.pyi]
[typing fixtures/typing-typeddict.pyi]

[case testLiteralAdditionGuardMaxValues]
from typing_extensions import Literal

HexDigit = Literal["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F"]

def foo(a: HexDigit, b: HexDigit, c: HexDigit) -> None:
reveal_type(a + b + c) # N: Revealed type is "builtins.str"
[builtins fixtures/primitives.pyi]
0