Introduction to Basf2PathTask

Hint

This example demonstrates how to create a simple b2luigi task that executes a basf2 simulation. The key points to be learned from this example are the Basf2PathTask class and create_path method.

For directly working with the Belle II Analysis Software Framework (basf2), b2luigi provides the Basf2PathTask task class. This class provides help for the user to create and execute a basf2 path. The Basf2PathTask also provides the following parameters that can be useful when executing basf2 processes:

• num_processes: number of parallel processes to use for the basf2 execution.

• max_event: maximum number of events to process. If set to 0, all events will be processed.

In contrast to the normal (b2)luigi tasks, the execution logic of a Basf2PathTask is not defined in a run method but in create_path. The create_path method needs to return the basf2 path that is created in the steering file. Furthermore, the Progress module is automatically added and print(b2.statistics) is called after the path is processed.

Warning

Due to technical reasons, the path needs to be created within the create_path method. The path can be used in further objects, however, it is not possible for it to originate from an outer scope.

Additional tips:

• For later porpuses, we add a parameter (identifier) to identify the output file uniqley. This is useful when running multiple tasks in parallel.

• We make use of the task own settings via result_dir. It is sometimes more useful to structure the output of your tasks in task specific directories than solely in the parameter based directories. Additionally, good practice is to provide absolute paths instead of relative paths as we do in this example.

• No batch submission of this task will be done (batch_system = "local"), more will come in the next examples.

• The example relies again on the task’s own get_output_file_name method to generate the output file name.

import basf2 as b2
import generators as ge
import simulation as si

import b2luigi
from b2luigi.basf2_helper import Basf2PathTask


class SimulationTask(Basf2PathTask):
    n_events = b2luigi.IntParameter()
    event_type = b2luigi.Parameter(default="mumu")
    identifier = b2luigi.Parameter(default="sample")

    result_dir = "results/Simulation"
    batch_system = "local"

    def output(self):
        yield self.add_to_output("simulation.root")

    def create_path(self):
        main = b2.Path()

        # Set number of events (optional: also set experiment and run number)
        main.add_module("EventInfoSetter", evtNumList=[self.n_events])
        decfile = (
            "./decfiles/BptoKpJpsi_JpsitoMuMu.dec"
            if str(self.event_type) == "mumu"
            else "./decfiles/BptoKpJpsi_JpsitoEE.dec"
        )
        # Signal generation
        ge.add_evtgen_generator(
            path=main, finalstate="signal", signaldecfile=b2.find_file(decfile), eventType=self.event_type
        )

        # Simulation
        si.add_simulation(path=main)

        # Write out simulation output to root file.
        main.add_module("RootOutput", outputFileName=self.get_output_file_name("simulation.root"))

        return main


if __name__ == "__main__":
    b2luigi.process(SimulationTask(n_events=10))