Simplify Union type alias in optuna/samplers/_cmaes.py#6478
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c-bata merged 2 commits intooptuna:masterfrom Feb 26, 2026
Merged
Simplify Union type alias in optuna/samplers/_cmaes.py#6478c-bata merged 2 commits intooptuna:masterfrom
c-bata merged 2 commits intooptuna:masterfrom
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Replace `Union[cmaes.CMA, cmaes.SepCMA, cmaes.CMAwM]` with the PEP 604 `cmaes.CMA | cmaes.SepCMA | cmaes.CMAwM` syntax and remove the unused `from typing import Union` import. This is safe because the type alias lives inside a `TYPE_CHECKING` block that is never evaluated at runtime. Addresses optuna#4508.
mypy does not recognize `X | Y` as a type alias without explicit TypeAlias annotation, unlike Union[X, Y] which is implicitly treated as one. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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LGTM. Thank you for your contribution.
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Motivation
Contributes to #4508.
Among the 8 files listed as "cannot be updated" in the issue,
_cmaes.pyis the only one where theUnionusage is exclusively inside aTYPE_CHECKINGblock (line 35). SinceTYPE_CHECKINGisFalseat runtime, the|union syntax is never evaluated by the interpreter — it is only seen by static type checkers, which fully support it regardless of the Python version.This is distinct from the other remaining files (e.g.,
_grid.py,_typing.py,distributions.py,probability_distributions.py), whereUnionappears in runtime type aliases that would fail on Python 3.9 if converted to|.Description of the changes
Union[cmaes.CMA, cmaes.SepCMA, cmaes.CMAwM]withcmaes.CMA | cmaes.SepCMA | cmaes.CMAwMinside theif TYPE_CHECKING:blockfrom typing import Unionimport