Returning EINTR from pthread semaphore or lock acquisition is an optional POSIX
feature. musl does not provide this feature, so some threadsignal tests fail
when Python is built against it.

There's no good way to test for musl, so we skip if we're on Linux and not using
glibc pthreads.

Also, hedge in the threading documentation about when we can provide interrupts
from lock acquisition.

* raise exception if _missing_ returns None or invalid type

Store a weak reference to stream readerfor breaking strong references

It breaks the strong reference loop between reader and protocol and allows to detect and close the socket if the stream is deleted (garbage collected)

* Fix enum members getting shadowed by parent attributes
* Move Enum._convert to EnumMeta._convert_
* Deprecate _convert

Improve Enum docs.


https://bugs.python.org/issue33437

In distutils.command.install, replace "pliant children" (previously,
it was "pliant slaves") with "helpers".

<!-- issue-number: [bpo-34605](https://www.bugs.python.org/issue34605) -->
https://bugs.python.org/issue34605
<!-- /issue-number -->

It is unused.

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Address a C undefined behavior signed integer overflow issue in set object table resizing.  Our -fwrapv compiler flag and practical reasons why sets are unlikely to get this large should mean this was never an issue but it was incorrect code that generates code analysis warnings.

<!-- issue-number: [bpo-1621](https://www.bugs.python.org/issue1621) -->
https://bugs.python.org/issue1621
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When handling \s, \d, or \w (and their inverse) escapes in bytes regexes this a small but measurable performance improvement.

<!-- issue-number: [bpo-34636](https://www.bugs.python.org/issue34636) -->
https://bugs.python.org/issue34636
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Followup to 90fc8980.

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This reverts commit 886483e2.

GCC complains:

Python/pylifecycle.c: In function ‘_Py_InitializeFromConfig’:
Python/pylifecycle.c:900:13: warning: ‘interp’ may be used uninitialized in this function [-Wmaybe-uninitialized]
         err = _Py_InitializeMainInterpreter(interp, &main_config);
         ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This seems spurious since &interp is passed to _Py_InitializeCore. Anyway, we
can easily initialize to quiet the warning.

closes bpo-31902: Fix the col_offset attribute for ast.Async* nodes to point to the "async" keyword. (GH-4175)

Previously, col_offset points to the keyword after "async".

Python 3.x does not fall back to comparing object addresses when comparing two `dt` objects.

<!-- issue-number: [bpo-34365](https://www.bugs.python.org/issue34365) -->
https://bugs.python.org/issue34365
<!-- /issue-number -->

closes bpo-31608: Fix a crash in methods of a subclass of _collections.deque with a bad __new__(). (GH-3788)

The default value of asyncio.StreamReader *limit* is `_DEFAULT_LIMIT` instead of `None`.

<!-- issue-number: [bpo-34613](https://www.bugs.python.org/issue34613) -->
https://bugs.python.org/issue34613
<!-- /issue-number -->

<!-- issue-number: [bpo-28617](https://www.bugs.python.org/issue28617) -->
https://bugs.python.org/issue28617
<!-- /issue-number -->

Although the kernel accepts any negative value for timeout, the
documented value to block indefinitely is -1.

This commit also makes the code similar to select.poll.poll().

Rewritten/updated sections:

* Event Loop APIs
* Transports & Protocols
* Streams
* Exceptions
* Policies
* Queues
* Subprocesses
* Platforms

8621bb5d sets the filename in directly in the FileNotFoundError, so we may revert the earlier fix 5f780400.

Mention the implicit cache in struct.Struct() docs.

Consistent with the re.compile documentation note.