The arguments to a generator function which is declared as a
contextmanager are stored inside the context manager, and
thus are kept alive, even when it is used as a regular context
manager, and not as a function decorator (where it needs
the original arguments to recreate the generator on each
call).

This is a possible unnecessary memory leak, so this changes
contextmanager.__enter__ to release the saved arguments,
as that method being called means that particular CM instance
isn't going to need to recreate the underlying generator.

Patch by Martin Teichmann.

Add PEP 557 Data CLasses to What's New.

Class authors no longer need to specify repr=False if they want to provide a custom __repr__ for dataclasses. The same thing applies for the other dunder methods that the dataclass decorator adds. If dataclass finds that a dunder methods is defined in the class, it will not overwrite it.

On mac, sendfile throws ENOTCONN on a repeated sendfile call if
the connection is closed. Normalize it to behave like other systems.

Travis when merging changes from a pull request onto the target branch
does not perform a rebase, instead it does a simple merge which causes
the PR commits to retain their commit dates. This means that the commit
log can potentially look like:

PR merge <-- HEAD
normal master commit <- master
more commits from normal workflow
PR commit 1
another master commit
PR commit 2

Performing a git diff from PR commit 2 to master will accidentally
include files that should not be there.

Closes python/core-workflow#14

Mention in the documentation of settrace and setprofile that errors in the
registered handlers will cause themselves unset.

bpo-31399: Let OpenSSL verify hostname and IP

The ssl module now uses OpenSSL's X509_VERIFY_PARAM_set1_host() and
X509_VERIFY_PARAM_set1_ip() API to verify hostname and IP addresses.

* Remove match_hostname calls
* Check for libssl with set1_host, libssl must provide X509_VERIFY_PARAM_set1_host()
* Add documentation for OpenSSL 1.0.2 requirement
* Don't support OpenSSL special mode with a leading dot, e.g. ".example.org" matches "www.example.org". It's not standard conform.
* Add hostname_checks_common_name
Signed-off-by: Christian Heimes <christian@python.org>

Add close(fd) function to the socket module
Signed-off-by: Christian Heimes <christian@python.org>

The hmac module now has hmac.digest(), which provides an optimized HMAC
digest for short messages. hmac.digest() is up to three times faster
than hmac.HMAC().digest().
Signed-off-by: Christian Heimes <christian@python.org>

Make it clear that setting __class__ on a module has worked since 3.5,
but support for __getattr__ and __dir__ on module instances requires 3.7+

Patch by Cheryl Sabella.

The nismodule is now compatible with new libnsl and headers location
Signed-off-by: Christian Heimes <christian@python.org>

Since context.c is compiled with Py_BUILD_CORE, using a macro
will result in a slightly more optimal code.

When an unawaited coroutine is collected very late in shutdown --
like, during the final GC at the end of PyImport_Cleanup -- then it
was triggering an interpreter abort, because we'd try to look up the
"warnings" module and not only was it missing (we were prepared for
that), but the entire module system was missing (which we were not
prepared for).

I've tried to fix this at the source, by making the utility function
get_warnings_attr robust against this in general. Note that it already
has the convention that it can return NULL without setting an error,
which is how it signals that the attribute it was asked to fetch is
missing, and that all callers already check for NULL returns.

There's a similar check for being late in shutdown at the top of
warn_explicit, which might be unnecessary after this fix, but I'm not
sure so I'm going to leave it.

* Document `from __future__ import annotations`
* Provide plumbing and tests for `from __future__ import annotations`
* Implement unparsing the AST back to string form

This is required for PEP 563 and as such only implements a part of the
unparsing process that covers expressions.

dictview_repr(): Use a Py_ReprEnter() / Py_ReprLeave() pair to check
for recursion, and produce "..." if so.

test_recursive_repr(): Check for the string rather than a
RecursionError.  (Test cannot be any tighter as contents are
implementation-dependent.)

test_deeply_nested_repr(): Add new test, replacing the original
test_recursive_repr().  It checks that a RecursionError is raised in
the case of a non-recursive but deeply nested structure.  (Very
similar to what test_repr_deep() in test/test_dict.py does for a
normal dict.)

OrderedDictTests: Add new test case, to test behavior on OrderedDict
instances containing their own values() or items().

Reported by Coverity Scan.

Global variables should not used as import target.
Use temporary variable instead.

Patch by Bo Bayles.

* bpo-32662: Implement Server.start_serving() and Server.serve_forever()

New methods:

* Server.start_serving(),
* Server.serve_forever(), and
* Server.is_serving().

Add 'start_serving' keyword parameter to loop.create_server() and
loop.create_unix_server().

The refleak in question wasn't really important, as context vars
are usually created at the toplevel and live as long as the interpreter
lives, so the context var name isn't ever GCed anyways.

Some tests failed when the PATH environment variable contained a path
to an existing file. Fix tests to ignore also NotADirectoryError, not
only FileNotFoundError and PermissionError.