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How to add handlers at runtime

You can configure handlers in two phases:

  1. Build a logger first with get_daq_logger(...).
  2. Add more handlers/filters later, based on runtime context.

This is useful in long-running services where extra outputs (for example ERS Kafka) should only be attached after additional configuration becomes available.

Add one handler at a time with add_handler

Use add_handler if you want to attach a single handler type to an existing logger.

from daqpytools.logging import HandlerType, add_handler, get_daq_logger

log = get_daq_logger(
    logger_name="existing_logger",
    rich_handler=True,
    stream_handlers=False,
)

# Add stdout stream handler later
add_handler(log, HandlerType.Lstdout, use_parent_handlers=True)

log.info("Now routes to rich + stdout by default")

Suppress by default with fallback_handler={HandlerType.Unknown}

You can make newly-added handlers opt-in only by setting fallback handlers to HandlerType.Unknown. This means records without explicit extra["handlers"] will not be emitted by those handlers.

from daqpytools.logging import HandlerType, add_handler, get_daq_logger

log = get_daq_logger("fallback_demo", rich_handler=True, stream_handlers=False)

# Add stderr handler, but suppress it by default
add_handler(
    log,
    HandlerType.Lstderr,
    use_parent_handlers=True,
    fallback_handler={HandlerType.Unknown},
)

log.critical("Only rich by default")

# Explicitly target stderr when needed
log.critical(
    "Rich + stderr when explicitly requested",
    extra={"handlers": [HandlerType.Rich, HandlerType.Lstderr]},
)

Passing arguments to handlers and filters via **kwargs

Advanced setup functions accept extra keyword arguments and forward them to the relevant handler/filter factories.

  • get_daq_logger(..., **extras) forwards extras to handler/filter construction.
  • add_handler(..., **extras) forwards extras to that handler factory.

Common examples:

  • file handler: path="mylog.log"
  • ERS Kafka handler: ers_kafka_session=...
  • throttle filter: initial_threshold=..., time_limit=...
  • rich handler: width=...

Example with explicit extras:

from daqpytools.logging import HandlerType, add_handler, get_daq_logger

log = get_daq_logger("extras_demo", rich_handler=False)

# Pass file-specific kwargs to file handler
add_handler(
    log,
    HandlerType.File,
    use_parent_handlers=True,
    path="extras_demo.log",
)

# Pass rich-specific kwargs to rich handler
add_handler(
    log,
    HandlerType.Rich,
    use_parent_handlers=True,
    width=120,
)

# ERS-specific kwargs are supplied through setup/get APIs
# setup_daq_ers_logger(log, ers_kafka_session="session_tester")