dist/tools/headerguards: fix flake8 issues

[aabadie]

Contribution description

This PR fixes the flake8 issues reported on the headerguards.py script.

Issues/PRs references

None

[kaspar030]

this changes semantics

[aabadie]

indeed, so fix_headerguard should return True at the end ?

[kaspar030]

fix_headerguard() returns "False" on error. The call site checks for that. Why change?

[aabadie]

Why change?

flake8 --config=dist/tools/flake8/flake8.cfg dist/tools/headerguards/
...
dist/tools/headerguards/headerguards.py:80:38: E712 comparison to False should be 'if cond is False:' or 'if not cond:'

I chose the second solution, because it's cleaner: fix_headerguard() should explicitly return True when problems are detected, False otherwise.

[kaspar030]

Then why not if fix_headerguard() is False:?

it's cleaner: fix_headerguard() should explicitly return True when problems are detected, False otherwise.

debatable.

[aabadie]

in general explicit is better than implicit. With the first suggestion, the function returns None when problems are detected, False otherwise. Testing between False and None could lead to confusion and buggy code. That's why I chose the other proposition.

[kaspar030]

The code was explicit before you broke it. And why returning True on error leads to less confusion than returning False is something I don't think you'll find in any style guide.

The function could return True when there's no error. Would that improve readability? I doubt it.

[aabadie]

Let's not spend too much time on this and move forward. I've just updated the PR with your preference.

[cladmi]

Its basically a function that would benefit from being split in parts and the error case done with an exception, but its another PR.