Formatting and filtering

Updated Nov 11, 2025

Logger-level formatting is fixed ("{logger} [LEVEL] message"). To customize output wrap handlers with formatter callables using the builder API:

def json_formatter(record: dict[str, object]) -> str:
    import json
    return json.dumps(
        {
            "logger": record["logger"],
            "level": record["level"],
            "message": record["message"],
        },
        separators=(",", ":"),
    )

stream = StreamHandlerBuilder.stdout().with_formatter(json_formatter).build()

Formatter identifiers are limited to "default" for now. Future releases will connect FormatterBuilder and handler formatter IDs, but this is not yet implemented.
Filters are only available through ConfigBuilder. dictConfig and fileConfig deliberately reject filter declarations so the limited, guaranteed-safe subset remains obvious.