twotasks.py

import luigi

class MyFirstTask(luigi.Task): # inherit from Luigi base class Task

    def run(self):
        with self.output().open('w') as f:
            f.write("This is my first task.\n")
            
    def output(self):
        return luigi.LocalTarget('MyTask.txt')

class MySecondTask(luigi.Task):
    # MyFirstTask() needs to run first
    def requires(self):
        return MyFirstTask()

    def run(self):
        # here we're going to count the words in the first file
        # and output it to a second file
        numwords = 0
        # once MyFirstTask() has run, this file has the info we need
        # it could just as easily be database output in here
            for line in f:
                words = line.split(None) # this splits on whitespace of any length
                numwords += len(words)

        # print our results
        with open('words.txt', 'w') as out:
            out.write(str(numwords)+"\n")

    def output(self):
        return luigi.LocalTarget('words.txt')

if __name__ == '__main__':

    # since we are setting MySecondTask to be the main task,
    # it will check for the requirements first, then run
    luigi.run(["--local-scheduler"], main_task_cls=MySecondTask)

Hi, I was trying your demo, and it seems there're some mistakes in the code.
Wrong Indentiation:
# it could just as easily be database output in here
for line in f:
words = line.split(None) # this splits on whitespace of any length
numwords += len(words)
Also, it seems f is not defined in MySecondTask, shouldn't you define it somewhere?
Let me know if you can advise me here. Thanks!

If you fix the indentation on lines 23-25 and change
for line in f:
to
for line in self.input().open('r'):

The script should then run.