It adds a missing testcase for bpo-34125. This is testing code which is
affected by PEP 590, so missing this test might accidentally break
CPython if we screw up with implementing PEP 590.

Add new sys.unraisablehook() function which can be overridden to
control how "unraisable exceptions" are handled. It is called when an
exception has occurred but there is no way for Python to handle it.
For example, when a destructor raises an exception or during garbage
collection (gc.collect()).

Changes:

* Add an internal UnraisableHookArgs type used to pass arguments to
  sys.unraisablehook.
* Add _PyErr_WriteUnraisableDefaultHook().
* The default hook now ignores exception on writing the traceback.
* test_sys now uses unittest.main() to automatically discover tests:
  remove test_main().
* Add _PyErr_Init().
* Fix PyErr_WriteUnraisable(): hold a strong reference to sys.stderr
  while using it

See also PR GH-13148.

The ``__rmod__`` method of ``collections.UserString`` class had a bug that made it unusable. 


https://bugs.python.org/issue25652

Co-Authored-By: Yury Selivanov <yury@magic.io>

Add an extend action to argparse


https://bugs.python.org/issue23378

Links creating an infinite symlink loop would raise an exception.

* bpo-36929: Modify io/re tests to allow for missing mod name

For a vanishingly small number of internal types, CPython sets the
tp_name slot to mod_name.type_name, either in the PyTypeObject or the
PyType_Spec. There are a few minor places where this surfaces:

* Custom repr functions for those types (some of which ignore the
  tp_name in favor of using a string literal, such as _io.TextIOWrapper)
* Pickling error messages

The test suite only tests the former. This commit modifies the test
suite to allow Python implementations to omit the module prefix.

https://bugs.python.org/issue36929

The mmap module set MAP_SHARED flag when map anonymous memory, however VxWorks
only support MAP_PRIVATE when map anonymous memory, this commit clear MAP_SHARED
and set MAP_PRIVATE.

This reverts commit 4959c33d.

Include windows.h rather than crtdbg.h to get STATUS_CONTROL_C_EXIT constant.
Moreover, include windows.h on Windows, not only when MSC is used.

* This PR fixes the `RuntimeWarning` in `inspect.isawaitable(mock())` where `mock()` was not awaited.
* Fix typo in asynctest project.

.. And update some deprecation warnings with version numbers.




https://bugs.python.org/issue36932

This parameter is marked as deprecated since 3.6 and for removal in 3.8.
It already had no effects.

https://bugs.python.org/issue23896

_PyRuntime.preconfig.coerce_c_locale can now be used to
check if the C locale has been coerced.

* Fix _Py_LegacyLocaleDetected(): don't attempt to coerce the
  C locale if LC_ALL environment variable is set. Add 'warn'
  parameter: emit_stderr_warning_for_legacy_locale() must not
  the LC_ALL env var.
* _PyPreConfig_Write() sets coerce_c_locale to 0 if
  _Py_CoerceLegacyLocale() fails.

* Fix encoding and locale tests in test_embed.InitConfigTests.
* InitConfigTests now only computes EXPECTED_CONFIG once.
* Add tests for PYTHONWARNINGS and PYTHONPATH env vars

This slightly expands an existing test case `test_popen_error` to trigger a `ResourceWarning` and fixes it.


https://bugs.python.org/issue35721

* Add _PyPreConfig.parse_argv
* Add _PyCoreConfig._config_init field and _PyCoreConfigInitEnum enum
  type
* Initialization functions: reject preconfig=NULL and config=NULL
* Add config parameter to _PyCoreConfig_DecodeLocaleErr(): pass
  config->argv to _Py_PreInitializeFromPyArgv(), to parse config
  command line arguments in preinitialization.
* Add config parameter to _PyCoreConfig_SetString(). It now
  preinitializes Python.
* _PyCoreConfig_SetPyArgv() now also preinitializes Python for wide
  argv
* Fix _Py_PreInitializeFromCoreConfig(): don't pass args to
  _Py_PreInitializeFromPyArgv() if config.parse_argv=0.
* Use "char * const *" and "wchar_t * const *" types for 'argv'
  parameters and _PyArgv.argv.
* Add unit test on preinitialization from argv.
* _PyPreConfig.allocator type becomes int
* Add _PyPreConfig_InitFromPreConfig() and
  _PyPreConfig_InitFromCoreConfig() helper functions

Print any argument other than None or int passed to SystemExit
or sys.exit().

Add new cpython/traceback.h and pycore_traceback.h header files to
Makefile.pre.in and PCbuild/ project.

Add new Include/cpython/traceback.h and Include/internal/traceback.h
header files.

The sqlit3.Connection object doesn't call its close() method when it's used
as a context manager.

* Add math.isqrt function computing the integer square root.

* Code cleanup: remove redundant comments, rename some variables.

* Tighten up code a bit more; use Py_XDECREF to simplify error handling.

* Update Modules/mathmodule.c
Co-Authored-By: Serhiy Storchaka <storchaka@gmail.com>

* Update Modules/mathmodule.c

Use real argument clinic type instead of an alias
Co-Authored-By: Serhiy Storchaka <storchaka@gmail.com>

* Add proof sketch

* Updates from review.

* Correct and expand documentation.

* Fix bad reference handling on error; make some variables block-local; other tidying.

* Style and consistency fixes.

* Add missing error check; don't try to DECREF a NULL a

* Simplify some error returns.

* Another two test cases:

- clarify that floats are rejected even if they happen to be
  squares of small integers
- TypeError beats ValueError for a negative float

* Add fast path for small inputs. Needs tests.

* Speed up isqrt for n >= 2**64 as well; add extra tests.

* Reduce number of test-cases to avoid dominating the run-time of test_math.

* Don't perform unnecessary extra iterations when computing c_bit_length.

* Abstract common uint64_t code out into a separate function.

* Cleanup.

* Add a missing Py_DECREF in an error branch. More cleanup.

* Update Modules/mathmodule.c

Add missing `static` declaration to helper function.
Co-Authored-By: Serhiy Storchaka <storchaka@gmail.com>

* Add missing backtick.