Task does not run Luigi

Question

i write a trivial piece of code to run the tasks in Luigi. The code is as bellow:

import luigi

count = 0

class TaskC(luigi.Task):
    def requires(self):
        return None

    def run(self):
        print("Running task C ...")
        global count
        with self.output().open('w') as outfile:
            outfile.write("Finished task C, count = %d", count)
            count += 1
        
    def output(self):
        return luigi.LocalTarget("./logs/task_c.txt")


class TaskB(luigi.Task):
    def requires(self):
        return None

    def run(self):
        print("Running task B ...")
        global count
        with self.output().open('w') as outfile:
            outfile.write("Finished task B, count = %d ...", count)
            count += 1
        
    def output(self):
        return luigi.LocalTarget("./logs/task_b.txt")


class TaskA(luigi.Task):

    def requires(self):
        return [TaskB(), TaskC()]

    def run(self):
        print("Running task A ...")
        global count
        with self.output().open('w') as outfile:
            outfile.write("Finished task A, count = %d ...", count)
            count += 1

    def output(self):
        return luigi.LocalTarget("./logs/task_a.txt")

if __name__ == '__main__':
    print("Start the fisrt luigi app :)")
    luigi.run()

Expect: i want to run TaskA, but TaskA requires TaskB and TaskC -> TaskB and TaskC should run before and first when both tasks B,C are finished, then TaskA can run

Actual: Only TaskA runs. The other tasks don't. The log in console:

Start the fisrt luigi app :)
DEBUG: Checking if TaskA() is complete
INFO: Informed scheduler that task   TaskA__99914b932b   has status   DONE
INFO: Done scheduling tasks
INFO: Running Worker with 1 processes
DEBUG: Asking scheduler for work...
DEBUG: Done
DEBUG: There are no more tasks to run at this time
INFO: Worker Worker(salt=382715991, workers=1, host=w10tng, username=tng, pid=2096) was stopped. Shutting down Keep-Alive thread
INFO:
===== Luigi Execution Summary =====

Scheduled 1 tasks of which:
* 1 complete ones were encountered:
    - 1 TaskA()

Did not run any tasks
This progress looks :) because there were no failed tasks or missing dependencies

===== Luigi Execution Summary =====

Command that i used to run:

python first_luigi_app.py --local-scheduler TaskA

I don't know if i've been missing somethings ! Would appreciate if some one can help :)

Answer 1

you can try removing requires methods from task B and task C as currently by returning None they are skipped. Also when using formatting with f-string it worked ok. Run with: python -m luigi --module l1 TaskA --local-scheduler where l1 is l1.py(copy of your code)