bpo-43651: Fix EncodingWarning in test_io

[methane]

https://bugs.python.org/issue43651

[methane]

This PR can be simplified after #25103 is merged.

[methane]

#25103 did not help OpenWrapper(). I don't think we should allow encoding="locale" in binmode only for test_io.

[vstinner]

I would prefer to replace all "ascii" with "utf-8". Come on, ASCII is now legacy!

[vstinner]

LGTM.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 FreeBSD Non-Debug 3.x has failed when building commit 58cffba.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/172/builds/124) and take a look at the build logs.
4. Check if the failure is related to this commit (58cffba) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/172/builds/124

Failed tests:

• test_asyncio

Failed subtests:

• test_stdin_stdout - test.test_asyncio.test_subprocess.SubprocessMultiLoopWatcherTests
• test_negative_lookahead - test.test_peg_generator.test_c_parser.TestCParser

Summary of the results of the build (if available):

== Tests result: FAILURE then FAILURE ==

406 tests OK.

10 slowest tests:

• test_smtpnet: 6 min 6 sec
• test_peg_generator: 4 min 44 sec
• test_nntplib: 4 min 31 sec
• test_concurrent_futures: 2 min 42 sec
• test_asyncio: 2 min 16 sec
• test_multiprocessing_forkserver: 2 min 5 sec
• test_multiprocessing_spawn: 2 min 2 sec
• test_urllib2: 2 min 1 sec
• test_tokenize: 1 min 39 sec
• test_unparse: 1 min 25 sec

1 test failed:
test_asyncio

20 tests skipped:
test_dbm_gnu test_devpoll test_epoll test_idle test_ioctl
test_msilib test_ossaudiodev test_readline test_spwd
test_startfile test_tcl test_tix test_tk test_ttk_guionly
test_ttk_textonly test_turtle test_winconsoleio test_winreg
test_winsound test_zipfile64

2 re-run tests:
test_asyncio test_peg_generator

Total duration: 18 min 28 sec

Click to see traceback logs

Traceback (most recent call last):
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/test/test_asyncio/test_subprocess.py", line 126, in run
    exitcode = await proc.wait()
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/asyncio/subprocess.py", line 134, in wait
    return await self._transport._wait()
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/asyncio/base_subprocess.py", line 235, in _wait
    return await waiter
asyncio.exceptions.CancelledError


Traceback (most recent call last):
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/test/test_peg_generator/test_c_parser.py", line 160, in test_negative_lookahead
    self.run_test(grammar_source, test_source)
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/test/test_peg_generator/test_c_parser.py", line 90, in run_test
    self.build_extension(grammar_source)
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/test/test_peg_generator/test_c_parser.py", line 87, in build_extension
    generate_parser_c_extension(grammar, Path(self.tmp_path))
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Tools/peg_generator/pegen/testutil.py", line 104, in generate_parser_c_extension
    compile_c_extension(str(source), build_dir=str(path))
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Tools/peg_generator/pegen/build.py", line 93, in compile_c_extension
    cmd.run()
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/distutils/command/build_ext.py", line 340, in run
    self.build_extensions()
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/distutils/command/build_ext.py", line 449, in build_extensions
    self._build_extensions_serial()
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/distutils/command/build_ext.py", line 474, in _build_extensions_serial
    self.build_extension(ext)
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/distutils/command/build_ext.py", line 529, in build_extension
    objects = self.compiler.compile(sources,
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/distutils/ccompiler.py", line 574, in compile
    self._compile(obj, src, ext, cc_args, extra_postargs, pp_opts)
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/distutils/unixccompiler.py", line 120, in _compile
    raise CompileError(msg)
distutils.errors.CompileError: command '/usr/bin/cc' failed with exit code -9


Traceback (most recent call last):
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/distutils/unixccompiler.py", line 117, in _compile
    self.spawn(compiler_so + cc_args + [src, '-o', obj] +
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/distutils/ccompiler.py", line 910, in spawn
    spawn(cmd, dry_run=self.dry_run)
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/distutils/spawn.py", line 87, in spawn
    raise DistutilsExecError(
distutils.errors.DistutilsExecError: command '/usr/bin/cc' failed with exit code -9


Traceback (most recent call last):
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/test/test_asyncio/test_subprocess.py", line 131, in test_stdin_stdout
    exitcode, stdout = self.loop.run_until_complete(task)
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/asyncio/base_events.py", line 641, in run_until_complete
    return future.result()
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/asyncio/tasks.py", line 460, in wait_for
    raise exceptions.TimeoutError() from exc
asyncio.exceptions.TimeoutError


Traceback (most recent call last):
  File "/usr/home/buildbot/python/3.x.koobs-freebsd-9e36.nondebug/build/Lib/asyncio/tasks.py", line 458, in wait_for
    fut.result()
asyncio.exceptions.CancelledError