(cherry picked from commit 4c7532e9)

(cherry picked from commit 4da52247)

* bpo-30876: Relative import from unloaded package now reimports the package
instead of failing with SystemError.

Relative import from non-package now fails with ImportError rather than
SystemError.
(cherry picked from commit 8a9cd20e)

* bpo-18018: Import raises ImportError instead of SystemError if a relative
import is attempted without a known parent package.

* bpo-26367: importlib.__init__() raises ImportError like
builtins.__import__() when ``level`` is specified but without an accompanying
package specified.

Cython will, in the right circumstances, offer a MethodType instance
where im_func is a builtin function. Any instance of MethodType is
automatically assumed to be a Python-defined function (more
specifically, a function that has an inspectable signature), but
_set_signature was still conservative in its assumptions. As a result
_set_signature would return early with None instead of a mock since
the im_func had no inspectable signature. This causes problems
deeper inside mock, as _set_signature is assumed to _always_
return a mock, and nothing checked its return value.

In similar corner cases, autospec will simply not check the spec of the
function, so _set_signature is amended to now return early with the
original, not-wrapped mock object.

Patch by Aaron Gallagher.

(cherry picked from commit 856cbcc1)

* Oops, tzdata was introduced in Python 3.6: remove it from regrtest
* Remove also Lib/test/libregrtest/__init__.py file: add by mistake
  on a backport.

When running the test suite using --use=all / -u all, exclude tzdata
since it makes test_datetime too slow (15-20 min on some buildbots)
which then times out on some buildbots.

-u tzdata must now be enabled explicitly, -u tzdata or -u all,tzdata,
to run all test_datetime tests.

Fix also regrtest command line parser to allow passing -u
extralargefile to run test_zipfile64.

Travis CI: remove -tzdata. Replace -u all,-tzdata,-cpu with -u all,-cpu since tzdata is now excluded from -u all.
(cherry picked from commit 5b392bba)

(cherry picked from commit fff2a210)

(cherry picked from commit 4ed5ad79)

(cherry picked from commit 49f6449e)

(cherry picked from commit 50f58163)

encoder and decoder.
(cherry picked from commit d3aaa2f1)

(cherry picked from commit f5232559)

Based on patch by Victor Stinner.
(cherry picked from commit 64e461be)

called with bytes-like argument.
(cherry picked from commit 1180e5a5)

Handle getattr(copy, 'deepcopy') error in _elementtree module
initialization.
(cherry picked from commit b136f11f)

multiprocessing.Queue.join_thread() now waits until the thread
completes, even if the thread was started by the same process which
created the queue.

Fix the following warning which occurs randomly when running
test_handle_called_with_mp_queue of test_logging.QueueListenerTest:

Warning -- threading_cleanup() failed to cleanup -1 threads after 4 sec (count: 0, dangling: 1)
(cherry picked from commit 3b69d911)

If history-length is set in .inputrc, and the history file is double the
history size (or more), history_get(N) returns NULL, and python
segfaults. Fix that by checking for NULL return value.

It seems that the root cause is incorrect handling of bigger history in
readline, but Python should not segfault even if readline returns
unexpected value.

This issue affects only GNU readline. When using libedit emulation
system history size option does not work.

Leading whitespace was incorrectly dropped during folding of certain lines in the _header_value_parser's folding algorithm.  This makes the whitespace handling code consistent.

(cherry picked from commit be5ebe58)

(cherry picked from commit 76c567ee)

* bpo-30855: Trying to fix test_use on Windows.

Avoid possible weird behavior of WideInt convertion.
"winfo id" always returns string hexadecimal representation.

(cherry picked from commit b9d67249)

* bpo-30855: Trying to fix test_use on Windows.

(cherry picked from commit 29a2f7c6)

(cherry picked from commit 7526cadd)

FXpy doesn't have a Python 3 port and it only
supports Python 2.2 and older versions.

Reported by Alex Walters on docs@p.o.

(cherry picked from commit d3ed2877)

(cherry picked from commit 8a8d2850)

* [3.6] bpo-29512, bpo-30776: Backport regrtest enhancements from master to 3.6 (#2513)

* bpo-29512: Add test.bisect, bisect failing tests (#2452)

Add a new "python3 -m test.bisect" tool to bisect failing tests.

It can be used to find which test method(s) leak references, leak
files, etc.
(cherry picked from commit 84d9d14a)

* bpo-30776: regrtest: reduce memleak false positive (#2484)

Only report a leak if each run leaks at least one memory block.
(cherry picked from commit beeca6e1)

(cherry picked from commit a3ca94d0)

* bpo-30764: Fix regrtest --fail-env-changed --forever (#2536) (#2539)

--forever now stops if a fail changes the environment.
(cherry picked from commit 5e87592f)
(cherry picked from commit 4132adb4)

Improve the description of the high and low parameters for set_write_buffer_limits.
Also fixed a small grammatical issue.
(cherry picked from commit 5200a7c7)

* bpo-30280: asyncio now cleans up threads

asyncio base TestCase now uses threading_setup() and
threading_cleanup() of test.support to cleanup threads.

* asyncio: Fix TestBaseSelectorEventLoop cleanup

bpo-30280: TestBaseSelectorEventLoop of
test.test_asyncio.test_selector_events now correctly closes the event
loop: cleanup its executor to not leak threads.

Don't override the close() method of the event loop, only override
the_close_self_pipe() method.

(cherry picked from commit b9030674)

bpo-11798, bpo-16662, bpo-16935, bpo-30813: Skip
test_discover_with_module_that_raises_SkipTest_on_import() and
test_discover_with_init_module_that_raises_SkipTest_on_import() of
test_unittest when hunting reference leaks using regrtest.
(cherry picked from commit e4f9a2d2)

* bpo-30807: signal.setitimer() may disable the timer by mistake

* Add NEWS blurb
(cherry picked from commit 729780a8)

* Clear potential ref cycle between Process and Process target

Besides Process.join() not being called, this was an indirect cause of bpo-30775.
The threading module already does this.

* Add issue reference.
(cherry picked from commit 79d37ae9)

Forgetting to call Process.join() can keep some resources alive.
(cherry picked from commit a79f8fac)

Based on patch by Victor Stinner.

Add private C API function _PyUnicode_AsUnicode() which is similar to
PyUnicode_AsUnicode(), but checks for null characters..
(cherry picked from commit f7eae0ad)

Clarify that the break statement breaks out of the innermost enclosing for or while loop.
(cherry picked from commit 36fc8967)

[3.5] bpo-30708: Add private C API function _PyUnicode_AsWideCharString(). (GH-2285) (GH-2443)  (#2448)

And use it instead of PyUnicode_AsWideCharString() if appropriate.

_PyUnicode_AsWideCharString(unicode) is like PyUnicode_AsWideCharString(unicode, NULL), but
raises a ValueError if the wchar_t* string contains null characters.
(cherry picked from commit e613e6ad).
(cherry picked from commit 0edffa30)

* bpo-30523: regrtest --list-cases --match (#2401)

* regrtest --list-cases now supports --match and --match-file options.
  Example: ./python -m test --list-cases -m FileTests test_os
* --list-cases now also sets support.verbose to False to prevent
  messages to stdout when loading test modules.
* Add support._match_test() private function.
(cherry picked from commit ace56d58)

* bpo-30764: regrtest: add --fail-env-changed option (#2402)

* bpo-30764: regrtest: change exit code on failure

* Exit code 2 if failed tests ("bad")
* Exit code 3 if interrupted

* bpo-30764: regrtest: add --fail-env-changed option

If the option is set, mark a test as failed if it alters the
environment, for example if it creates a file without removing it.

(cherry picked from commit 63f54c68)

* bpo-30776: reduce regrtest -R false positives (#2422)

* Change the regrtest --huntrleaks checker to decide if a test file
  leaks or not. Require that each run leaks at least 1 reference.
* Warmup runs are now completely ignored: ignored in the checker test
  and not used anymore to compute the sum.
* Add an unit test for a reference leak.

Example of reference differences previously considered a failure
(leak) and now considered as success (success, no leak):

    [3, 0, 0]
    [0, 1, 0]
    [8, -8, 1]
(cherry picked from commit 48b5c422)