The requires decorator

Hint

This example demonstrates how to create a simple b2luigi task that executes the reconstruction of previously simulated events. The key point of this example is the requires decorator.

We start with the usual imports. Note that we import the task SimulationTask class defined in the previous example Introduction to Basf2PathTask: it’s generally recommended to keep your code as much modular as possible.

import basf2 as b2
import reconstruction as re
import mdst

import b2luigi
from b2luigi.basf2_helper import Basf2PathTask
from Ex05_basf2_simulation import SimulationTask

Here me make use of the requires decorator to require the SimulationTask. This functionality is very useful when the dependencies of tasks are very easily defined. The task with the requires decorator will automatically create the requires method that returns the required task. Additionally, the task also inherits all the parameters of the required task.

@b2luigi.requires(SimulationTask)
class ReconstructionTask(Basf2PathTask):
    result_dir = "results/Reconstruction"
    batch_system = "local"

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

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

        # Read the simulated events that were created in the simulation task.
        main.add_module("RootInput", inputFileNames=self.get_input_file_names("simulation.root"))

        # Run reconstruction
        main.add_module("Gearbox")
        main.add_module("Geometry")
        re.add_reconstruction(main)

        # Add MDST output.
        mdst.add_mdst_output(path=main, filename=self.get_output_file_name("reconstruction.root"))
        return main

As already pointed out in the second example, here we only need to call the ReconstructionTask: the scheduler will resolves all the required dependencies.

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