(cherry picked from commit d6238a76)

[2.7] bpo-30347: Stop crashes when concurrently iterate over itertools.groupby() iterators. (GH-1557). (#3772)

(cherry picked from commit c740e4fe)

(cherry picked from commit 0e950dd2)

Patch by Raymond Hettinger.

Non-regression tests for the Expat 2.2.3 UTF-8 decoder bug.

(cherry picked from commit e6d9fcbb)

Previously ensurepip would always report success, even if the
pip installation failed.

(cherry picked from commit 9adda0cd)

Use prefixed macro names for the `authoraddress` function, add T2A to the font encoding in LaTeX sources to support Cyrillic characters in the PDF documentation, and replace the deprecated `font_size` config option with `pointsize`.
(cherry picked from commit da9b4cfb)

(cherry picked from commit 19e4d934)

(cherry picked from commit da67e0d6)

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

[2.7] bpo-31471: Fix assertion failure in subprocess.Popen() on Windows, in case env has a bad keys() method. (GH-3580) (#3595)

This no-op change makes 2.7 more consistent with 3.x to ease comparison and backports.

(cherry picked from commit 1de4705d)

fork_wait.py tests now joins threads, to not leak running threads in
the background.

(cherry picked from commit c99d41f9)

(cherry picked from commit 71fe8c00)

[2.7] bpo-31411: Prevent raising a SystemError in case warnings.onceregistry is not a dictionary. (GH-3485). (#3493)

(cherry picked from commit 252033d5)

(cherry picked from commit 2e6bb448)

ttk.OptionMenu radiobuttons weren't unique 
between instances of OptionMenu.
(cherry picked from commit a568e527)

Patch by Paul.j3.  Includes an unrelated but useful addition to the
optparse porting section.
(cherry picked from commit 0c7983e4)

* bpo-29136: Add TLS 1.3 support

TLS 1.3 introduces a new, distinct set of cipher suites. The TLS 1.3
cipher suites don't overlap with cipher suites from TLS 1.2 and earlier.
Since Python sets its own set of permitted ciphers, TLS 1.3 handshake
will fail as soon as OpenSSL 1.1.1 is released. Let's enable the common
AES-GCM and ChaCha20 suites.

Additionally the flag OP_NO_TLSv1_3 is added. It defaults to 0 (no op) with
OpenSSL prior to 1.1.1. This allows applications to opt-out from TLS 1.3
now.

Signed-off-by: Christian Heimes <christian@python.org>.
(cherry picked from commit cb5b68ab)

Signed-off-by: Christian Heimes <christian@python.org>
(cherry picked from commit 17c9ac92)

Also provide a solution if the user wants to keep multiple blank lines.
(cherry picked from commit 397c467c)

See also 1f29cefc.  The configure.ac change was omitted from the earlier change...

Signed-off-by: Christian Heimes <christian@python.org>.
(cherry picked from commit d3b9f97e)

Signed-off-by: Christian Heimes <christian@python.org>
(cherry picked from commit ad0ffa03)

(cherry picked from commit 8204b903)

This also eliminats a dead link to Weave in the process..
(cherry picked from commit 78ffd6cf)

Fix copying of partial characters for UTF-8 input (libexpat bug 115):
https://github.com/libexpat/libexpat/issues/115

(cherry picked from commit 759e30ec)

The standard header stdbool.h is not available
with old Visual Studio compilers

Cherry-picked from libexpat b4b89c2ab0cc5325a41360c25ef9d2ccbe617e5c.

expat: Add artificial scopes in xmltok.c utf8_toUtf8() to fix c89 compilation.

Cherry-picked from libexpat commit e0b290eb3d8f4c4b45137a7d7f4f8db812145bd2

(cherry picked from commit f801322e)

* bpo-31339: Rewrite time.asctime() and time.ctime()

Backport and adapt the _asctime() function from the master branch to
not depend on the implementation of asctime() and ctime() from the
external C library. This change fixes a bug when Python is run using
the musl C library.

* bound checks for time.asctime()

* bound checks for time.strftime()

Really this time!

* bpo-27448: Work around a gc.disable race condition in subprocess.

This works around a gc.isenabled/gc.disable race condition in the 2.7
subprocess module by using a lock for the critical section.  It'll
prevent multiple simultaneous subprocess launches from winding up with
gc remaining disabled but it can't fix the ultimate problem: gc enable
and disable is a global setting and a hack.

Users are *strongly encouraged* to use subprocess32 from PyPI instead
of the 2.7 standard library subprocess module.  Mixing threads with
subprocess is a recipie for disaster otherwise even with "fixes" to
ameliorate common issues like this.

* Add a blurb!

(cherry picked from commit 8adc73c2)