Automerge-Triggered-By: @tiran

* Add example on lazy imports

* Use four spaces for indentation

* change to console

The phrase "At any time during execution," was repeated twice.

Automerge-Triggered-By: @Mariatta

…or (pythonGH-21474)

#msg373510

[bpo-32528]()/python#13528 changed `asyncio.CancelledError` such that it no longer inherits from `concurrent.futures.CancelledError`. As this affects existing code, specifically when catching the latter instead of the former in exception handling, it should be documented in the "What's new in 3.8?" document.

Automerge-Triggered-By: @1st1

…using recv_into instead of recv (python#21442)

* bpo-41273: Proactor transport read loop to use recv_into

By using recv_into instead of recv we do not allocate a new buffer each
time _loop_reading calls recv.

This betters performance for any stream using proactor (basically any
asyncio stream on windows).

* bpo-41273: Double proactor read transport buffer size

By doubling the read buffer size we get better performance.

Avoid infinite loop when reading specially crafted TAR files using the tarfile module
(CVE-2019-20907).

Move definition of UNUSED from modified headers of libmpdec to
_decimal.c itself. This makes the vendored source closer to the
standalone library and fixes build with --with-system-libmpdec.

Tested to build fine with either system libmpdec or the vendored one.

…thonGH-21718)

regrtest_unraisable_hook() temporarily replaces sys.stderr with
sys.__stderr__ to help to display errors when a test captures stderr.

incr cannot be larger than INT_MAX: downcast to int explicitly.

On Windows, fix asyncio recv_into() return value when the socket/pipe
is closed (BrokenPipeError): return 0 rather than an empty byte
string (b'').