* #30014: make selectors.DefaultSelector.modify() faster by relying on selector's modify() method instead of un/register()ing the fd

* #30014: add unit test

* speedup poll/epoll/devpoll modify() method by using internal modify() call

* update doc

* address PR comments

* update NEWS entries

* use != instead of 'is not'

Avoid a deadlock when the waiter who is about to take the lock is
cancelled

Issue #27585

* Fix regression in error message introduced in bpo-29951.

* Add test.

* Make the test more strong.

contextlib.AbstractContextManager now supports anti-registration
by setting __enter__ = None or __exit__ = None, following the pattern
introduced in bpo-25958.

Test C functions:

* _PyObject_FastCall()
* _PyObject_FastCallDict()
* _PyObject_FastCallKeywords()

* RFC 1750 has been been obsoleted by RFC 4086.
* RFC 3280 has been obsoleted by RFC 5280.
* RFC 4366 has been obsoleted by RFC 6066.

See discussion:
  https://github.com/python/cpython/pull/1992#issuecomment-307024778

* Add a new option taking a filename to get a list of test names to
  filter tests.
* support.match_tests becomes a list.
* Modify run_unittest() to accept to match the whole test identifier,
  not just a part of a test identifier.

For example, the following command only runs test_default_timeout()
of the BarrierTests class of test_threading:

$ ./python -m test -v test_threading -m test.test_threading.BarrierTests.test_default_timeout

Remove also some empty lines from test_regrtest.py to make flake8
tool happy.

'invalid character in identifier' now is raised instead of
'f-string: empty expression not allowed' if a subexpression contains
only whitespaces and they are not accepted by Python parser.

Fix a reference leak in _io._WindowsConsoleIO: PyUnicode_FSDecoder()
always initialize decodedname when it succeed and it doesn't clear
input decodedname object.

On Windows, subprocess.Popen.communicate() now also ignore EINVAL
on stdin.write() if the child process is still running but closed the
pipe.

The cell_contents attribute of the cell object is now writable.

Error messages when pass keyword arguments to some builtins that
don't support keyword arguments contained double parenthesis: "()()".
The regression was introduced by bpo-30534.

Fix a reference in subinterpreters, like test_callbacks_leak() of
test_atexit.

warnoptions is a list used to pass options from the command line to
the sys module constructor. Before this change, the list was shared
by multiple interpreter which is not the expected behaviour. Each
interpreter should have their own independent mutable world.

This change duplicates the list in each interpreter. So each
interpreter owns its own list, so each interpreter can clear its own
list.

Fix regressions introduced by:

- bpo-22257: commits 1abcf670 and 6b4be195Co-Authored-By: Victor Stinner <victor.stinner@gmail.com>
Co-Authored-By: Louie Lu <git@louie.lu>

If pass a server_hostname= that fails IDNA decoding to SSLContext.wrap_socket or SSLContext.wrap_bio, then the SSLContext object had a spurious Py_DECREF called on it, eventually leading to segfaults.

* bpo-30537: use PyNumber in itertools instead of PyLong

* bpo-30537: revert changes except to islice_new

* bpo-30537: test itertools.islice and add entry to Misc/NEWS

* Update config.{guess,sub} from gnu.org.

* Fix bpo-30584

* Adding a comment mentionning the bpo and explaining what is the identifier

* Add Denis Osipov to Misc/ACKS

Clarify that `two-pass` buffer can only be dumped once, and it prints out all text sent to it during all processing, even from Clinic blocks *after* the dumping point.

Replace `datetuil` into `dateutil`

On Windows 8, 8.1 and 10 at least, the exit code is the exception
code (no bit is cleared).

to functions implemented in C that don't support this.

Also unified error messages for functions that don't take positional or keyword
arguments.

Implemented pickling for loggers.

* Simplify X.509 extension handling code

The previous implementation had grown organically over time, as OpenSSL's API evolved.

* Delete even more code

Several class attributes have been added to calendar.HTMLCalendar that allow customization of the CSS classes used in the resulting HTML. This can be done by subclasses HTMLCalendar and overwriting those class attributes (Patch by Oz Tiram).

Also weakens the 'should this be run?' regex to allow all builds when .travis.yml changes.

* bpo-30557: faulthandler now correctly filters and displays exception codes on Windows

* Adds test for non-fatal exceptions.

* Adds bpo number to comment.

Update the code example in Functions and Methods section
Remove objtype argument in MethodType

Also on the short-lived `buildbot-custom` branch.

* bpo-30538: Update count() in Functional HOWTO

* bpo-30538: Update enumerate() arguments in Functional HOWTO