Fixed also testing the "always" warning filter.

Include a more easily understood example for nullcontext

This will prevent emitting a resource warning when the execution was
interrupted by Ctrl-C between calling open() and entering a 'with' block
in "with open()".

webbrowser._synthesize() called webbrowser.register() with
outdated signature.
Co-Authored-By: John Still <john@jmsdvl.com>

Make the change where discussing the CPython implementation of lists and dicts.

The 'output formatting' section of the tutorial talks a lot about manual formatting with things like .rjust() and .zfill(), with only a passing reference to 3.6's new f-strings.

This doesn't drop all of the old material, but it does rearrange the topics into a more modern order: f-strings first, discussing formatting specifiers a bit; then calling .format(); finally manual formatting with .ljust().

"can be used do declare" → "can be used to declare"

* Always return bytes from _HackedGetData.get_data().

Ensure the imp.load_source shim always returns bytes by reopening the file in
binary mode if needed. Hash-based pycs have to receive the source code in bytes.

It's tempting to change imp.get_suffixes() to always return 'rb' as a mode, but
that breaks some stdlib tests and likely 3rdparty code, too.

Stop using key=lambda.  This behavior is same to C version encoder.

The multiprocessing module now uses the monotonic clock
time.monotonic() instead of the system clock time.time() to implement
timeouts.

* converted bytes methods: expandtabs, ljust, rjust, center, zfill
* updated char_convertor to properly set the C default value

The line is speaking of a list of commands, not the list command.

Most of the change involves fixing up the test suite, which previously made
the assumption that there wouldn't be a new line if the input didn't end in
one.

Contributed by Ammar Askar.

tarfile._Stream has two buffer for compressed and uncompressed data.
Those buffers are not aligned so unnecessary bytes slicing happens
for every reading chunks.

This commit bypass compressed buffering.

In this benchmark [1], user time become 250ms from 300ms.

[1]: https://bugs.python.org/msg320763

Per the recommendation in our Developer's Guide:
  https://devguide.python.org/documenting/#paragraph-level-markup

subprocess.Popen now copies the startupinfo argument to leave it
unchanged: it will modify the copy, so that the same STARTUPINFO
object can be used multiple times.

Add subprocess.STARTUPINFO.copy() method.