Fix TabError for Python 3

[cclauss]

TabError: inconsistent use of tabs and spaces in indentation is treated as a syntax error in Python 3.

./example/reinforcement-learning/ddpg/strategies.py:65:39: E999 TabError: inconsistent use of tabs and spaces in indentation
        action = policy.get_action(obs)
                                      ^

[marcoabreu]

@simoncorstonoliver @ThomasDelteil any chance you guys can squeeze in example validation together with the tutorial validation? We're having a lot of problems in our examples that are hidden because we don't test them. This causes a quite bad first use experience.

[ThomasDelteil]

@marcoabreu that's a great idea. However examples have a very big variance in terms of code quality compared to tutorials, a lot of them would need a major rewrite in the process of being made testable. That's definitely something I would like to do at some point but the scale of it significantly larger than tutorials. (1)3 reasons why:

• Examples usually come with a bunch of arguments and problems are usually due to conflicting choices of script argument.
• Examples can come with a lot of dependencies, sometimes on dataset download, external resources that are most of the times not automated through code at the moment
• Examples are sometimes not end to end scripts but provide several utilities to achieve a specific task
  One thing we could do to make it more manageable is to survey them all, split them into manageable tasks and try to get a community push to resolve such tasks and increase the overall quality and have a more unified feel for our examples.
  We are currently going through the backlog of "Examples" "HowTo" "Question" "Docs" issues and aiming to close virtually all of them by the end of this quarter.

[marcoabreu]

Excellent, thanks a lot for this detailed answer! This definitely sounds like a good approach, do you think it would be possible to request adding it to your teams long term planning - maybe as part of Q3 and the efforts to resolve the example related issues? I think a lot of these issues are based on the fact that we don't have proper test coverage for them.

We could basically start with an example and create a small guide. Then we'd make a quick sprint where everybody takes one example and adds it to CI in accordance with your instructions.

[ThomasDelteil]

@marcoabreu can't really speak on behalf of @simoncorstonoliver but I think we have already planed out Q3 in terms of resource allocation so that might need to wait for Q4, and Q3 will focus on resolving outstanding problems that have been reported through the community github issues and questions on the forum, before moving to automated testing. That will depends also on how fast we can go through the backlog of issues while keeping up with the new ones that arise 😄

[cclauss]

@marcoabreu @ThomasDelteil Can you please review ("Files changed" --> "Review changes") this change because the goal of this PR is to make a simple whitespace-only change that is easy to review. However, much text has been written above that will cause reviewers to pause.

[marcoabreu]

Sorry, we just waited for CI to pass :)

[simoncorstonoliver]

@marcoabreu a good starting point point might be a review of the examples to see which ones properly belong in the repo. Some might be better as a blog posts with independent repo rather than something that is considered an integral part of the repo for the framework.

We spent time in Nov 2017 to ensure they all worked -- it proved to be more effort than we anticipated. So let's put it on the to-do list for consideration for Q4.

Alternatively of course we're flagging issues as needing attention from new contributors. Some examples might benefit from attention from new contributors with expertise in specific fields.