bpo-30485: Change the prefix for defining the default namespace in ElementPath from None to '' since there is existing code that uses that and it's more convenient to have an all-string-keys dict (e.g. when sorting items etc.). (#12860)

# [bpo-36651](https://bugs.python.org/issue36651): Fixed Asyncio Event Loop documentation inconsistency  

In the documentation for the call_later and the call_at methods there is a note which says that the delay cannot be longer than a day, but both methods have a note saying that this limitation was removed in Python 3.8
Here I fixed this issue by removing the pre-exising note and added a versionchanged. 

To test my changes I have rebuilt the documentation with ```make html```. I did not have any errors and the effected page displayed correctly on a browser.



https://bugs.python.org/issue36651

Add a new _testinternalcapi module to test the internal C API.

Move _Py_GetConfigsAsDict() function to the internal C API:
_testembed now uses _testinternalcapi to access the function.

This paragraph doesn't seem to be a part of code, but merged into previous code block.

Change PyAPI_FUNC(type), PyAPI_DATA(type) and PyMODINIT_FUNC macros
of pyport.h when Py_BUILD_CORE_MODULE is defined.

The Py_BUILD_CORE_MODULE define must be now be used to build a C
extension as a dynamic library accessing Python internals: export the
PyInit_xxx() function in DLL exports on Windows.

Changes:

* Py_BUILD_CORE_BUILTIN and Py_BUILD_CORE_MODULE now imply
  Py_BUILD_CORE directy in pyport.h.
* ceval.c compilation now fails with an error if Py_BUILD_CORE is not
  defined, just to ensure that Python is build with the correct
  defines.
* setup.py now compiles _pickle.c with Py_BUILD_CORE_MODULE define.
* setup.py compiles _json.c with Py_BUILD_CORE_MODULE define, rather
  than Py_BUILD_CORE_BUILTIN define
* PCbuild/pythoncore.vcxproj: Add Py_BUILD_CORE_BUILTIN define.

Fix Python Initialization code on FreeBSD to detect properly when
stdin file descriptor (fd 0) is invalid.

On FreeBSD, fstat() must be used to check if stdin (fd 0) is valid.
dup(0) doesn't fail if stdin is invalid in some cases.

Skip tests cases setting RLIMIT_FSIZE and RLIMIT_CPU on VxWorks.

subprocess.Popen doesn't support preexec on VxWorks.

Document the change in a NEWS entry of the Security category.

shutil.which() and distutils.spawn.find_executable() now use
os.confstr("CS_PATH") if available instead of os.defpath, if the PATH
environment variable is not set.

Don't use os.confstr("CS_PATH") nor os.defpath if the PATH
environment variable is set to an empty string to mimick Unix 'which'
command behavior.

Changes:

* find_executable() now starts by checking for the executable in the
  current working directly case. Add an explicit
  "if not path: return None".
* Add tests for PATH='' (empty string), PATH=':' and for PATHEXT.

 Fix test_tabnanny on VxWorks: adjust ENOENT error message,
use os.strerror().

It reduces "data" segment in python about 200KB.

Signed-off-by: Matthias Bussonnier <bussonniermatthias@gmail.com>

Use literalinclude markup to include Tools/scripts/serve.py code.
Tools/scripts/serve.py first argument on the command line is now optional.

IPv4Interface and IPv6Interface did not has netmask and hostmask
attributes when its argument is bytes or int.

This commit extracts method for constructors of Network and Interface,
and ensure Interface class always provides them.

The imap.IMAP4.logout() method no longer ignores silently arbitrary
exceptions.

Changes:

* The IMAP4.logout() method now expects a "BYE" untagged response,
  rather than relying on _check_bye() which raises a self.abort()
  exception.
* IMAP4.__exit__() now does nothing if the client already logged out.
* Add more debug info if test_logout() tests fail.

Don't assign generations[2].threshold to generations[2].threshold:
useless operation.

Move unstable CPython API from Include/pymem.h into a new
Include/cpython/pymem.h header file.

Keep the nudge towards DeprecationWarning, but remove the
"Note" markup and generally shorten the description.

Ref: https://github.com/python/cpython/pull/12505/files#r273978757

Remove left-over references to Python 3.0 as the future in Fraction class docstrings.

Fix test_imap4_host_default_value() of test_imaplib: catch also
errno.ENETUNREACH error.

time.clock() is not available on VxWorks.

* cached_property is more efficient than hand crafted cache.
* In IPv[46]Network, `self.network.prefixlen` is same to `self._prefixlen`.

bpo-30485: Re-allow empty strings in ElementPath namespace mappings since they might actually be harmless and unused (and thus went undetected previously). (#12830)

Add new keyword arguments "default_namespace" and "xml_declaration" to functions ET.tostring() and ET.tostringlist(), as known from ElementTree.write().

In Python having a trace function in effect while mock is imported causes isinstance to be wrong for MagicMocks. This is due to the usage of super() in some class methods, as this sets the __class__ attribute. To avoid this, as a workaround, alias the usage of super .

bpo-36427: Document that PyEval_RestoreThread and PyGILState_Ensure can terminate the calling thread (GH-12541)

Calling these function from a thread when the runtime is finalizing will terminate
the thread, even if the thread was not created by Python. Users can use 
_Py_IsFinalizing or sys.is_finalizing to check if the interpreter is in the process of
being finalized before calling this function to avoid unwanted termination.