fix all invalid escape sequences

[bluenote10]

Why are these changes needed?

This PR fixes all invalid escape sequences, and enables the corresponding flake8 rule W605.

This came up as part of #48921, leading to the wrong conclusion that the mypy hiccup is related to invalid escape sequences. Most likely it isn't (python/mypy#18215 (comment)), but it may still be a good idea to get rid of these to avoid unnecessary warnings and confusion.

I couldn't really figure out how flake8 is executed by the CI, because just running flake8 on the master branch actually fails, and running scripts/format.sh doesn't seem to do anything (most likely because it only checks the diff, and isn't a full check). So I'm wondering if enabling the W605 check currently actually has much of an effect.

Related issue number

Related to #48921

Checks

• I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
  • I've added any new APIs to the API Reference. For example, if I added a
    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[alexeykudinkin]

@bluenote10 thank you very much for doing the clean up!

Can you please take a look at the CI failures?

[bluenote10]

@bluenote10 thank you very much for doing the clean up!

With pleasure 😉

Can you please take a look at the CI failures?

Good catch: There were actually a few regexes where the \ was partially escaped and non-escaped. I've re-checked them all, and hope they are now all fixed.

[alexeykudinkin]

Wait, these aren't regexes

[bluenote10]

Yes, but docstrings can also contain invalid escape sequences. See for instance the noise coming out of mypy in #48921, which points to malformed docstrings.

I would assume that most likely these docstrings were written thinking that a \ is just a plain \, which raw string literals achieve.

[alexeykudinkin]

Right, but the solution isn't to annotate it as regex though, right?

Solution should be to escape the slash

[bluenote10]

What do you mean by "annotate it as regex"?

Using raw string literals like r"""...""" has nothing to do with regexes. They are just string literals where the \ is not used as an escape code for introducing special chars like \n or \r.

It just happens to be common to use raw string literals when writing regexes, because it often involves \ and the raw string literal avoid having to escape them all.

[richardliaw]

@alexeykudinkin could you take another pass at this?

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[pcmoritz]

Thanks a lot for working on this @bluenote10, let's get this merged if the tests pass :)

[pcmoritz]

@bluenote10 Thanks a lot for your contribution, and sorry for the delay in getting this merged 🎉