Cleanup code by removing if __name__ == '__main__' pattern

[Tarrasch]

This patch started out as fixing the red in the current travis flake8
step. As most occurrences was about simply removing the over-(mis)-used
if __name__ == "__main__" pattern that was way to prevalent in the luigi
code base.

This is kind of analogous to the other time flake8 suddenly got more
sensitive. See #1786

[mention-bot]

@Tarrasch, thanks for your PR! By analyzing the history of the files in this pull request, we identified @freider, @hadesbox and @erikbern to be potential reviewers.

[dlstadther]

@Tarrasch , Are you saying that $ luigi --module examples.foo examples.Foo --workers 2 --local-scheduler is the only "proper" way to execute luigi code and that if __name__ == '__main__' shouldn't be used? Why is this?

[Tarrasch]

I believe that to be the case yes. I think there's a few advantages:

• Less boilerplate
• Your file is even more "declarative". I think the luigi API should have a declarative feel, just like GNU make.
• Reading a line like python src/python/blah/blah/luigi_tasks.py ... feels like it could do anything, having something like luigi --module blah/blah/luigi_tasks ... is clearer that it's about starting luigi.
• Python community in general seem to be for "have only one way to do things". I don't like that we're currently not consistent in our docs and code.

Come to think about it. I made a similar statement when I deprecated luigi.run().

Does all this make sense to you? :)

[erikbern]

I don't mind the `if name == 'main`` personally. I generally hate overly prescriptive frameworks that impose rules on how to execute stuff. But I guess this is only internal cleanup so LGTM

[dlstadther]

Shoot, I'm just behind on the times then. Perhaps due to my comfort with Python, I've always used

if __name__ == "__main__":
    luigi.run(['NameOfMyTopLevelTask', '--some-option', 'the_value'])

Since I don't print or see my non-errors, I was unaware of luigi.run deprecation.

I'll switch over to luigi --module /path/to/file.py TaskName --option value

[Tarrasch]

Reviewers: Seems like the actual flake8 issues were fixed in a540006 already, thanks @mrunesson. :)

---

@dlstadther, I'm still not sure if luigi.run was a correct thing. Please feedback how using luigi plays out for you.

[erikbern]

@dlstadther in that case there's no need to involve command line parsing. iirc you can just do luigi.build([NameOfMyTask('banana')])