Fix the use of recursion in itertools.chain.from_iterable. Using recursion
is unnecessary, and can easily cause stack overflows, especially when
building in low optimization modes or with Py_DEBUG enabled.

when pass indices of wrong type.

Element.getiterator() and the html parameter of XMLParser() were
deprecated only in the documentation (since Python 3.2 and 3.4 correspondintly).
Now using them emits a deprecation warning.

* Don’t need check_warnings any more.

* test_normalization fails if download fails

bpo-29887. The test is still skipped if "-u urlfetch" option is not
passed to regrtest (python3 -m test -u urlfetch test_normalization).

* Fix ResourceWarning in test_normalization

bpo-29887: Fix ResourceWarning in test_normalization if tests are
interrupted by CTRL+c.

ValueError always is raised rather than OverflowError for negative counts.
Shifting zero with non-negative count always returns zero.

if pass `accept={int, NoneType}`.

os.fwalk() is sped up by 2 times by using os.scandir().

unlucky Unicode characters.

an exception raised at the very first of an iterable would cause pools behave abnormally
(swallow the exception or hang)

Add the 'monetary' parameter to format_string so that all
uses of format can be converted to format_string.  Adjust
the documentation accordingly, and add a deprecation
warning when format is used.

bpo-19824
bpo-20314
bpo-12518

The presence of the ``--enable-optimizations`` flag is indicated by the
value of ``$enableval``, but the configure script was checking ``$withval``,
resulting in the ``--enable-optimizations`` flag being effectively ignored.

Instead have gcc be used for the coverage build so gcc is exercised in at least one place.

bpo-23890: unittest.TestCase.assertRaises() now manually breaks a
reference cycle to not keep objects alive longer than expected.

* DOC: clarify documentation for `round`

Clarified that `round` can take a negative value for *ndigits*.

* DOC: remove trailing whitespace in previous commit

remove trailing whitespace in previous commit

Make also minor PEP8 coding style fixes on modified imports.

* Remove unused test file

* Remove duplicated text in sndhdrdata README