* Refactor Parser/pgen and add documentation and explanations

To improve the readability and maintainability of the parser
generator perform the following transformations:

    * Separate the metagrammar parser in its own class to simplify
      the parser generator logic.

    * Create separate classes for DFAs and NFAs and move methods that
      act exclusively on them from the parser generator to these
      classes.

    * Add docstrings and comment documenting the process to go from
      the grammar file into NFAs and then DFAs. Detail some of the
      algorithms and give some background explanations of some concepts
      that will helps readers not familiar with the parser generation
      process.

    * Select more descriptive names for some variables and variables.

    * PEP8 formatting and quote-style homogenization.

The output of the parser generator remains the same (Include/graminit.h
and Python/graminit.c remain untouched by running the new parser generator).

bpo-36311: Fixes decoding multibyte characters around chunk boundaries and improves decoding performance (GH-15083)

Special characters in email address header display names are normally
put within double quotes. However, encoded words (=?charset?x?...?=) are
not allowed withing double quotes. When the header contains a word with
special characters and another word that must be encoded, the first one
must also be encoded.

In the next example, the display name in the From header is quoted and
therefore the comma is allowed; in the To header, the comma is not
within quotes and not encoded, which is not allowed and therefore
rejected by some mail servers.

From: "Foo Bar, France" <foo@example.com>
To: Foo Bar, =?utf-8?q?Espa=C3=B1a?= <foo@example.com>





https://bugs.python.org/issue37482

bpo-37663: have venv activation scripts all consistently use __VENV_PROMPT__ for prompt customization (GH-14941)

The activation scripts generated by venv were inconsistent in how they changed the shell's prompt. Some used `__VENV_PROMPT__` exclusively, some used `__VENV_PROMPT__` if it was set even though by default `__VENV_PROMPT__` is always set and the fallback matched the default, and one ignored `__VENV_PROMPT__` and used `__VENV_NAME__` instead (and even used a differing format to the default prompt). This change now has all activation scripts use `__VENV_PROMPT__` only and relies on the fact that venv sets that value by default.

The color of the customization is also now set in fish to the blue from the Python logo for as hex color support is built into that shell (much like PowerShell where the built-in green color is used).

bpo-37834: Normalise handling of reparse points on Windows
* ntpath.realpath() and nt.stat() will traverse all supported reparse points (previously was mixed)
* nt.lstat() will let the OS traverse reparse points that are not name surrogates (previously would not traverse any reparse point)
* nt.[l]stat() will only set S_IFLNK for symlinks (previous behaviour)
* nt.readlink() will read destinations for symlinks and junction points only

bpo-1311: os.path.exists('nul') now returns True on Windows
* nt.stat('nul').st_mode is now S_IFCHR (previously was an error)

Added back mention that ensure_future actually scheduled obj. This documentation just mentions what ensure_future returns, so I did not realize that ensure_future also schedules obj.

Fix codecs.lookup() to normalize the encoding name the same way
than encodings.normalize_encoding(), except that codecs.lookup()
also converts the name to lower case.

* add netlify deploy preview

* fix publish path

* install python3 venv

* add sudo

* try without venv

* install right dependencies

* use python3, not python

* use pip3

* python3.7

* use requirements.txt

* move requirements.txt to Doc

* use python 3.7 in runtime.txt

* move runtime.txt

* Update requirements.txt

The faulthandler module no longer allocates its alternative stack at
Python startup. Now the stack is only allocated at the first
faulthandler usage.

faulthandler no longer ignores memory allocation failure when
allocating the stack. sigaltstack() failure now raises an OSError
exception, rather than being ignored.

The alternative stack is no longer used if sigaction() is
not available. In practice, sigaltstack() should only be available
when sigaction() is avaialble, so this change should have no effect
in practice.

faulthandler.dump_traceback_later() internal locks are now only
allocated at the first dump_traceback_later() call, rather than
always being allocated at Python startup.

Fixed wrong link to Telnet.open() method in telnetlib documentation.

* Write a message when killing a worker process
* Put a timeout on the second popen.communicate() call
  (after killing the process)
* Put a timeout on popen.wait() call
* Catch popen.kill() and popen.wait() exceptions

There are plenty of legitimate scripts in the tree that begin with a
`#!`, but also a few that seem to be marked executable by mistake.

Found them with this command -- it gets executable files known to Git,
filters to the ones that don't start with a `#!`, and then unmarks
them as executable:

    $ git ls-files --stage \
      | perl -lane 'print $F[3] if (!/^100644/)' \
      | while read f; do
          head -c2 "$f" | grep -qxF '#!' \
          || chmod a-x "$f"; \
        done

Looking at the list by hand confirms that we didn't sweep up any
files that should have the executable bit after all.  In particular

 * The `.psd` files are images from Photoshop.

 * The `.bat` files sure look like things that can be run.
   But we have lots of other `.bat` files, and they don't have
   this bit set, so it must not be needed for them.



Automerge-Triggered-By: @benjaminp

If this service had thoroughly vanished, we could just ignore the
test until someone gets around to either recreating such a service
or redesigning the test to somehow work locally.  The
`support.transient_internet` mechanism catches the failure to
resolve the domain name, and skips the test.

But in fact the domain snakebite.net does still exist, as do its
nameservers -- and they can be quite slow to reply.  As a result
this test can easily take 20-30s before it gets auto-skipped.

So, skip the test explicitly up front.

_get_socket() already prints a debug message for the host and port.



https://bugs.python.org/issue32793



Automerge-Triggered-By: @maxking

Implement PyBuffer_SizeFromFormat() function (previously
documented but not implemented): call struct.calcsize().

pymalloc_alloc() now returns directly the pointer, return NULL on
memory allocation error.

allocate_from_new_pool() already uses NULL as marker for "allocation
failed".

* Minor documentation fixes on library/enum

This reverts commit d3dcc927.

Add threading.Thread.__del__() method to ensure that the thread state
lock is removed from the _shutdown_locks list when a thread
completes.

Because mod, func, class, etc all share one namespace, :func:time creates a link to the time module doc page rather than the time.time function.

* Add a minor `Fraction.__hash__` optimization that got lost in the shuffle.

Document the optimizations.

The fact that keyword names are strings is now part of the vectorcall and `METH_FASTCALL` protocols. The biggest concrete change is that `_PyStack_UnpackDict` now checks that and raises `TypeError` if not.

CC @markshannon @vstinner 


https://bugs.python.org/issue37540

Without indendation, seems like strcpy line is parallel to `if` condition.

Base PR for other PRs that want to play with `type.__call__` such as #13930 and #14589.

The author is really @markshannon I just made the PR.


https://bugs.python.org/issue37207



Automerge-Triggered-By: @encukou

Replace usage of the obscure PEM_read_bio_X509_AUX with the more standard PEM_read_bio_X509 (GH-15303)



X509_AUX is an odd, note widely used, OpenSSL extension to the X509 file format. This function doesn't actually use any of the extra metadata that it parses, so just use the standard API.

Automerge-Triggered-By: @tiran