Codecov Report

Merging #2919 into master will decrease coverage by 10.74%.
The diff coverage is 36.90%.

@@             Coverage Diff             @@
##           master    #2919       +/-   ##
===========================================
- Coverage   63.30%   52.55%   -10.75%     
===========================================
  Files         466      249      -217     
  Lines       20893    15472     -5421     
  Branches     2901        0     -2901     
===========================================
- Hits        13226     8132     -5094     
- Misses       7301     7340       +39     
+ Partials      366        0      -366     

Thanks for taking the time doing this and submitting the pull request!
Oh boy, that are a ton of changes (+1,859 −2,728)...

Just a couple of early thoughts from my side after a first quick review:

• It would probably be better to split this up into more commits, for reviewing reasons. One commit for each operation pyupgrade supports, for example, if it's possible, similar to Flake8 #2804. This would also be better for the commit history, git blame, etc...
• The string format related changes are probably unneeded or rather too much, as they only make explicit string templates implicit. Also, there's the 3.5 support drop in September, which enables the usage of f-strings once we go >=3.6, making these changes therefore a bit redundant.
• The included flashmedia package still has a compat file with py2 stuff, even though some of its files were modified.
• The order of imports in some modules has changed after the removal of the compat module. There's no linting rule for that here and not really important now, just wanted to mention it though.
• By removing one python version from the build matrix in the GH workflow file, the CodeCov comment threshold also needs to be changed in its config file. (not important now)

I would say the first change should be to update the docs and disallow Python 2 installs by updating setup.py and setup.cfg to remove the Python 2 specifics.

I believe that setup.cfg needs to be updated to remove this:

[wheel]
universal = 1

Perhaps a guard in setup.py needs to be added, something like

if sys.version_info < (3, 5):
    sys.exit('streamlink is only supported on Python 3.5 and later')

Once it is only possible to install streamlink on Python 3, then we can remove the Python 2 cruft.

It would be nice to target Python 3.6+, but I don't know if that will be popular :)

Thanks for the comments! Yeah, it's a big one!

PR #2920 is a minimal version of this, with the first commit from here, plus a few bits from the last commit here, plus @beardypig's suggestions.

Then we can deal with fine-grained pyupgrade and the compat replacements separately.

The order of imports in some modules has changed after the removal of the compat module. There's no linting rule for that here and not really important now, just wanted to mention it though.

I've found https://github.com/timothycrosley/isort/ great for taking the hassle out this.

#3270 already has all compat imports removed.