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Make filename, stream, and handlers parameters of logging.basicConfig mutually-exclusive #15435

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Make filename, stream, and handlers parameters of logging.basicConfig mutually-exclusive #15435

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3d67314
Add overloads for mutually-exclusive `logging.basicConfig` parameters
brianschubert Feb 16, 2026
1cdd578
Allow inert `filemode` when `handlers=None`
brianschubert Feb 16, 2026
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18 changes: 18 additions & 0 deletions stdlib/@tests/test_cases/check_logging.py
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Original file line number Diff line number Diff line change
Expand Up @@ -28,3 +28,21 @@ def record_factory(*args: Any, **kwargs: Any) -> logging.LogRecord:
logging.handlers.QueueListener(queue.Queue())
logging.handlers.QueueListener(queue.SimpleQueue())
logging.handlers.QueueListener(multiprocessing.Queue())

# These all raise at runtime.
logging.basicConfig(filename="foo.log", handlers=[]) # type: ignore
logging.basicConfig(filemode="w", handlers=[]) # type: ignore
logging.basicConfig(stream=None, handlers=[]) # type: ignore
logging.basicConfig(filename="foo.log", stream=None) # type: ignore
logging.basicConfig(filename=None, stream=None) # type: ignore
# These are ok.
logging.basicConfig()
logging.basicConfig(handlers=[])
logging.basicConfig(filename="foo.log", filemode="w")
logging.basicConfig(filename="foo.log", filemode="w", handlers=None)
logging.basicConfig(stream=None)
logging.basicConfig(stream=None, handlers=None)
# 'filemode' is inert when 'filename' is not passed, but is accepted if 'handlers=None'.
logging.basicConfig(filemode="w", stream=None)
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@srittau srittau Feb 17, 2026

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This sounds like a case where we could forbid filemode to prevent an error where users pass it, expecting to do something when it doesn't. But I don't have strong feelings either way.

# dubious but accepted, has same meaning as 'stream=None'.
logging.basicConfig(filename=None)
30 changes: 28 additions & 2 deletions stdlib/logging/__init__.pyi
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Original file line number Diff line number Diff line change
Expand Up @@ -576,16 +576,42 @@ if sys.version_info >= (3, 11):
def getLevelNamesMapping() -> dict[str, int]: ...

def makeLogRecord(dict: Mapping[str, object]) -> LogRecord: ...
@overload # handlers is non-None
def basicConfig(
*,
format: str = ..., # default value depends on the value of `style`
datefmt: str | None = None,
style: _FormatStyle = "%",
level: _Level | None = None,
handlers: Iterable[Handler],
force: bool | None = False,
encoding: str | None = None,
errors: str | None = "backslashreplace",
) -> None: ...
@overload # handlers is None, filename is passed (but possibly None)
def basicConfig(
*,
filename: StrPath | None,
filemode: str = "a",
format: str = ..., # default value depends on the value of `style`
datefmt: str | None = None,
style: _FormatStyle = "%",
level: _Level | None = None,
handlers: None = None,
force: bool | None = False,
encoding: str | None = None,
errors: str | None = "backslashreplace",
) -> None: ...
@overload # handlers is None, filename is not passed
def basicConfig(
*,
filename: StrPath | None = None,
filemode: str = "a",
format: str = ..., # default value depends on the value of `style`
datefmt: str | None = None,
style: _FormatStyle = "%",
level: _Level | None = None,
stream: SupportsWrite[str] | None = None,
handlers: Iterable[Handler] | None = None,
handlers: None = None,
force: bool | None = False,
encoding: str | None = None,
errors: str | None = "backslashreplace",
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