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Type narrowing for unions Literal | uuid.UUID doesn't work #18569
Description
Bug Report
When using the union of Literal type and uuid.UUID as a type, after comparing with a literal value, the value does not narrow to the type uuid.UUID.
However, this behavior is observed only when uuid.UUID is used as the type. If other types, such as built-ins and custom classes, are used instead, the comparison with a literal value results in the value narrowing to the appropriate type.
To Reproduce
https://mypy-play.net/?mypy=1.14.1&python=3.13&gist=04f8465218eabef5641c72b78e4a7e67
from typing import Literal
from uuid import UUID
type TLiteral = Literal["text"]
TEXT: TLiteral = "text"
# type T = int # works good
type T = UUID # fails
def f(v: T | TLiteral) -> T | None:
if v == TEXT:
return None
return vExpected Behavior
Success: no issues found in 1 source file
Actual Behavior
error: Incompatible return value type (got "UUID | Literal['text']", expected "UUID | None"
Your Environment
- Mypy version used: 1.14.1
- Mypy command-line flags:
- Mypy configuration options from
mypy.ini(and other config files):
[tool.mypy]
plugins = ["pydantic.mypy"]
check_untyped_defs = true
enable_error_code = "explicit-override,unused-awaitable,ignore-without-code,truthy-bool,possibly-undefined,redundant-expr,redundant-self"
pretty = true
show_error_context = true
strict = true
warn_unreachable = true- Python version used: 3.13
Activity
A5rocks commentedon Jan 30, 2025
Reproduce without
uuid(and with less concepts):I think the negative narrowing of
==for literals is incorrect here.A5rocks commentedon Jan 30, 2025
Duplicate of #16465