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Run a task

Within the Fractal framework, tasks are run as executable commands with a given signature, which looks like 

python task.py --args-json /path/to/arguments.json --out-json /path/to/output/metadata.json

The run_fractal_task wrapper converts a Python function into such a command-line interface. It can be used by writing a task Python module like

my_task.py
from pydantic import validate_call

@validate_call
def my_task(
    zarr_url: str,
    argument_1: int,
):
    # This is the task function, which performs some image-processing task
    # ...

if __name__ == "__main__":
    from fractal_task_tools.task_wrapper import run_fractal_task
    run_fractal_task(task_function=my_task)
where the if __name__ == "__main__" block at the end is the one introducing the proper command-line interface.

Log configuration

By default, the task wrapper sets a default format (%(asctime)s; %(name)s; %(levelname)s; %(message)s) and a default logging level (INFO) loggers based on the Python logging library. As an example, when running the following updated version of the example above

my_task_with_logs.py
import logging
from pydantic import validate_call

logger = logging.getLogger("my_task_with_logs")

@validate_call
def my_task_with_logs(
    zarr_url: str,
    argument_1: int,
):
    # This is the task function, which performs some image-processing task
    # ...

    logger.debug(f"Here is a DEBUG log from the task.")
    logger.info(f"Here is an INFO log from the task.")
    logger.warning("Here is a WARNING log from the task")

if __name__ == "__main__":
    from fractal_task_tools.task_wrapper import run_fractal_task
    run_fractal_task(task_function=my_task_with_logs)
the logs look like 
2026-02-10 09:31:33,338; run_fractal_task; INFO; START my_task task
2026-02-10 09:31:33,338; my_task_with_logs; INFO; Here is an INFO log from the task.
2026-02-10 09:31:33,339; my_task_with_logs; WARNING; Here is a WARNING log from the task
2026-02-10 09:31:33,339; run_fractal_task; INFO; END my_task task

The task developer can fully disable any logging configuration in the task wrapper by calling it as in 

run_fractal_task(task_function=my_task_with_logs, skip_logging_configuration=True)

The task user can customize the default format and logging level by setting any of the following environment variables:

  • FRACTAL_TASK_LOG_LEVEL, which must be a value in DEBUG, INFO, WARNING, ERROR, or CRITICAL.
  • FRACTAL_TASK_LOG_FORMAT, which must be in the same style as the default value (%(asctime)s; %(name)s; %(levelname)s; %(message)s) and can include any attribute from https://docs.python.org/3/library/logging.html#logrecord-attributes.
  • FRACTAL_TASK_SKIP_LOG_CONFIG: whenever this is set (to any arbitrary value), it has the same effect as skip_logging_configuration=True.