Make test_imap4_host_default_value independent on whether the 
local IMAP server is running.

bpo-35972: _xxsubinterpreters: Fix potential integer truncation on 32-bit in channel_send() (gh-11822)

Changes in this commit:

1. Use a _strong_ reference between the Pool and associated iterators
2. Rework PR #8450 to eliminate a cycle in the Pool.

There is no test in this commit because any test that automatically tests this behaviour needs to eliminate the pool before joining the pool to check that the pool object is garbaged collected/does not hang. But doing this will potentially leak threads and processes (see https://bugs.python.org/issue35413).

If PyUnicode_DecodeUTF8() returns NULL, PyArena_AddPyObject() would crash.
Found by @msullivan for https://github.com/python/typed_ast/pull/93.

Original patch by Mike Short


https://bugs.python.org/issue22062

Keeping references to processes and managers between tests makes them count as dangling processes.

Add  a code example block.

Add tooling that will useful in future updates, paying particular attention to difficult cases where only the upper bits on the input vary.

Use autoconfig to probe for shm_open() and shm_unlink().  Set SHM_NEEDS_LIBRT if we must
link with librt to get the shm_* functions.  Change setup.py to use the autoconfig defines.  These
changes should make it more likely that _multiprocessing/posixshmem.c gets built correctly on
different platforms.

This was a backwards incompatible change and should be clearly noted.

Related bugs:

bpo-32417: https://bugs.python.org/issue32417
bpo-35364: https://bugs.python.org/issue35364

Protect dict iterations by wrapping them with _IterationGuard in the
following methods:

- WeakValueDictionary.copy()
- WeakValueDictionary.__deepcopy__()
- WeakKeyDictionary.copy()
- WeakKeyDictionary.__deepcopy__()

Add a cell constructor, expose the cell type in the types module.

bpo-24209: In http.server script, rely on getaddrinfo to bind to preferred address based on the bind parameter. (#11767)

In http.server script, rely on getaddrinfo to bind to preferred address based on the bind parameter.

As a result, now IPv6 is used as the default (including IPv4 on dual-stack systems). Enhanced tests.

multiprocessing: provide unittests for manager classes and shareable types

* bpo-35321: Set the spec origin to frozen in frozen modules

This fix correctly sets the spec origin to
"frozen" for the _frozen_importlib module. Note that the
origin was already correctly set in _frozen_importlib_external.

* 📜🤖 Added by blurb_it.

* Make timedelta return subclass types

Previously timedelta would always return the `date` and `datetime`
types, regardless of what it is added to. This makes it return
an object of the type it was added to.

* Add tests for timedelta arithmetic on subclasses

* Make pure python timedelta return subclass types

* Add test for fromtimestamp with tz argument

* Add tests for subclass behavior in now

* Add news entry.

Fixes:
bpo-32417
bpo-35364

* More descriptive variable names in tests

Addresses Victor's comments

Python 3.8.0a1

After reading __PYVENV_LAUNCHER__ we now set sys._base_executable value for later use.
Make the same changes for macOS to avoid extra platform checks.

bpo-35692: pathlib no longer raises when checking file and directory existence on drives that are not ready (GH-11746)