Modernize codebase to python 3.7+ standard

[harahu]

This PR is the result of a one-off run of pyupgrade on the trio code base.

For future reference, this was done by running the following command from the project root:

find . -name '*.py' -exec pyupgrade --py3-only --py37-plus {} +

I also ran black in preview mode (black --preview), which mainly results in string cleanup.

[codecov]

Codecov Report

Merging #2480 (df093eb) into master (fc0932a) will increase coverage by 0.86%.
The diff coverage is 98.11%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2480      +/-   ##
==========================================
+ Coverage   97.99%   98.85%   +0.86%     
==========================================
  Files         118      118              
  Lines       16222    16222              
  Branches     3143     3143              
==========================================
+ Hits        15896    16037     +141     
+ Misses        264      131     -133     
+ Partials       62       54       -8     

Impacted Files	Coverage Δ
trio/_abc.py	100.00% <ø> (ø)
trio/_core/_asyncgens.py	100.00% <ø> (ø)
trio/_core/_local.py	98.11% <0.00%> (ø)
trio/_core/tests/test_asyncgen.py	99.06% <ø> (ø)
trio/_core/tests/test_multierror.py	100.00% <ø> (ø)
trio/_core/tests/test_run.py	100.00% <ø> (ø)
trio/_threads.py	100.00% <ø> (ø)
trio/_util.py	100.00% <ø> (ø)
trio/tests/test_channel.py	100.00% <ø> (ø)
trio/tests/test_dtls.py	99.79% <ø> (ø)
... and 37 more

[Fuyukai]

I'm in favour of merging this because I like blank lines and double quotes, but I'm not sure if the higher-ups will like it.

[harahu]

@Fuyukai My thinking is that you are already using black. So might as well apply it properly across the code base.

[harahu]

I hope this can be merged. I'm realizing that it might seem daunting to review this, given the diff size, but the tools I've used are conservative w.r.t modifying behavior, so the changes should be relatively safe.

[pquentin]

@Fuyukai as a member, you get to approve and merge this if you like it!

[harahu]

I hope it can be merged. I want to make further changes on top of this.

[pquentin]

Thanks! Can you please exclude notes-to-self?

[harahu]

Thanks! Can you please exclude notes-to-self?

@pquentin I've done so now. I get one failing test suite, but I think it might be a case of test flakiness? What is your take?

[pquentin]

Not sure what's going on sorry. I've relaunched the Ubuntu 3.7 tests a few times and it appears to fail consistently which is concerning.

[harahu]

Not sure what's going on sorry. I've relaunched the Ubuntu 3.7 tests a few times and it appears to fail consistently which is concerning.

I'll see if I can figure out what is going on. Perhaps later today.

[pquentin]

I can confirm that the Ubuntu 3.7 failures are not specific to this pull request.

[harahu]

I can confirm that the Ubuntu 3.7 failures are not specific to this pull request.

Thanks @pquentin! Was scratching my head over this one.

[pquentin]

Would you mind opening a pull request that skips this test on Ubuntu and Python 3.7 specifically? I can only imagine that a fix in more recent versions was not backported there. I don't want to invest time in debugging this, especially when Python 3.7 won't be supported anymore in 7 months, and this is blocking us.

[harahu]

Looks like this one is finally good to go! Thank you so much for all the help @pquentin!

[pquentin]

LGTM! Thanks for your patience.

[pquentin]

(I'll let you click on the green merge button yourself!)