* Trivial cleanups following bpo-31370

* Also cleanup the "importlib._bootstrap_external" module

* bpo-31499, xml.etree: Fix xmlparser_gc_clear() crash

xml.etree: xmlparser_gc_clear() now sets self.parser to NULL to prevent a
crash in xmlparser_dealloc() if xmlparser_gc_clear() was called previously
by the garbage collector, because the parser was part of a reference cycle.
Co-Authored-By: Serhiy Storchaka <storchaka@gmail.com>

This reverses a never-released regression resulting from bpo-31287.

This function returns the last component of tp_name after a dot.
Returns tp_name itself if it doesn't contain a dot.

bpo-31482: Missing bytes support for random.seed() version 1 #3614

Shorten the comment to: "using integer format specifier"

bpo-31490: Fix an assertion failure in ctypes in case an _anonymous_ attr is defined only outside _fields_. (#3615)

Canceling timers prevents a warning message when test_idle completes.
(This is the minimum fix needed before upcoming releases.)

Provide additional examples of using format specifiers in f-strings
Added examples for using integer and date format specifiers.

When apply changes, call .reload on each class with non-key options.
Change ParenMatch so that updates affect current instances.

The concrete PyDict_* API is used to interact with PyInterpreterState.modules in a number of places. This isn't compatible with all dict subclasses, nor with other Mapping implementations. This patch switches the concrete API usage to the corresponding abstract API calls.

We also add a PyImport_GetModule() function (and some other helpers) to reduce a bunch of code duplication.

Signed-off-by: Christian Heimes <christian@python.org>

Replaces PROTOCOL_TLSv* and PROTOCOL_SSLv23 with PROTOCOL_TLS_CLIENT and
PROTOCOL_TLS_SERVER.
Signed-off-by: Christian Heimes <christian@python.org>

SSLSocket.wrap_bio() and SSLSocket.wrap_socket() hard-code SSLObject and
SSLSocket as return types. In the light of future deprecation of
ssl.wrap_socket() module function and direct instantiation of SSLSocket,
it is desirable to make the return type of SSLSocket.wrap_bio() and
SSLSocket.wrap_socket() customizable.
Signed-off-by: Christian Heimes <christian@python.org>

'Strip trailing whitespace' is not limited to spaces.  Wording caters to beginners who
do know know the meaning of 'whitespace'.  Multiline string literals are not skipped.

* News blurb.

Give 30 seconds to join_process(), instead of 5 or 10 seconds, to
wait until the process completes.

Call the .join() method of threading.Timer timers to prevent the
"threading_cleanup() failed to cleanup 1 threads" warning.

* Add Py_UNREACHABLE() as an alias to abort().
* Use Py_UNREACHABLE() instead of assert(0)
* Convert more unreachable code to use Py_UNREACHABLE()
* Document Py_UNREACHABLE() and a few other macros.

Enabled by default was a temporary expedient.  The fix is to add a user override to enable.

New -n flag allow overriding localhost with custom value,
for example to run from containers.

Fix Coverity CID 1417587: _PyMem_Initialize() contains code which is
never executed.

Replace the runtime check with a build assertion.

join_thread() joins a thread but raises an AssertionError if the
thread is still alive after timeout seconds.

Call thread.join() to prevent the "dangling thread" warning.

Use _thread.count() to wait until threads exit. The new context
manager prevents the "dangling thread" warning.

Call thread.join() to prevent the "dangling thread" warning.

* Avoid calling "PyObject_GetAttrString()" (and potentially executing user code) with a live exception set.

* Ignore only AttributeError on attribute lookups in ElementTree.XMLParser() and propagate all other exceptions.

bpo-31471: Fix assertion failure in subprocess.Popen() on Windows, in case env has a bad keys() method. (#3580)

This makes the default behavior (without specifying `globalns` manually) more
predictable for users, finds the right globalns automatically.

Implementation for classes assumes has a `__module__` attribute and that module
is present in `sys.modules`.  It does this recursively for all bases in the
MRO.  For modules, the implementation just uses their `__dict__` directly.

This is backwards compatible, will just raise fewer exceptions in naive user
code.

Originally implemented and reviewed at https://github.com/python/typing/pull/470.

A bunch of code currently uses PyInterpreterState.modules directly instead of PyImport_GetModuleDict(). This complicates efforts to make changes relative to sys.modules. This patch switches to using PyImport_GetModuleDict() uniformly. Also, a number of related uses of sys.modules are updated for uniformity for the same reason.

Note that this code was already reviewed and merged as part of #1638. I reverted that and am now splitting it up into more focused parts.

* bpo-31234: Join threads in test_hashlib

Use thread.join() to wait until the parallel hash tasks complete
rather than using events. Calling thread.join() prevent "dangling
thread" warnings.

* test_hashlib: minor PEP 8 coding style fixes

Call thread.join() on threads to prevent the "dangling threads"
warning.