'\0' is the NUL byte not NULL.

* Add 'tstate' parameter to many internal import.c functions.
* _PyImportZip_Init() now gets 'tstate' parameter rather than
  'interp'.
* Add 'interp' parameter to _PyState_ClearModules() and rename it
  to _PyInterpreterState_ClearModules().
* Move private _PyImport_FindBuiltin() to the internal C API; add
  'tstate' parameter to it.
* Remove private _PyImport_AddModuleObject() from the C API:
  use public PyImport_AddModuleObject() instead.
* Remove private _PyImport_FindExtensionObjectEx() from the C API:
  use private _PyImport_FindExtensionObject() instead.

I didn't find any entries in the docs about these functions, so I just mentioned them, in "What's New".

* Add Include/cpython/import.h and Include/internal/pycore_import.h
  header files.
* Move _PyImport_ReInitLock() to the internal C API. Don't export the
  symbol anymore.

Tab now moves focus across and down for Help Source and Custom Run.

Also adds abalkin to CODEOWNERS for date and time related files.

For datetime.datetime.strptime(), the leading zero for some two-digit formats is optional.

This adds a footnote to the strftime/strptime documentation to reflect this fact, and adds some tests to ensure that it is true.

bpo-34903

default case ought to handle the "unexpected".

The initialize options are 1) add command line options, which are appended to sys.argv as if passed on a real command line, and 2) skip the shell restart. The customization dialog is accessed by a new entry on the Run menu.

Many PyRun_XXX() functions like PyRun_String() were no longer
exported in libpython38.dll by mistake. Export them again to fix the
ABI compatibiliy.

test_pre_initialization_sys_options() of test_embed now removes
PYTHON* environment variables like PYTHONWARNINGS.

aifc.openfp() alias to aifc.open(), sunau.openfp() alias to
sunau.open(), and wave.openfp() alias to wave.open() have been
removed. They were deprecated since Python 3.7.

Mainly, add a doc reference to message in pyshell.

Measure required height by quickly maximizing once per screen.
A search for a better method failed.

Add --upgrade-deps to venv module
- This allows for pip + setuptools to be automatically upgraded to the latest version on PyPI
- Update documentation to represent this change

bpo-34556: Add --upgrade to venv module

Explain in the doc why PyObject_CallNoArgs() should be preferred over
other existing ways to call a function without any arguments.

Other implementation can raise MemoryError, but it can takes hours.

Mention explicitly that PyObject_CallXXX() functions raise an
exception an failure.

Add a new public PyObject_CallNoArgs() function to the C API: call a
callable Python object without any arguments.

It is the most efficient way to call a callback without any argument.
On x86-64, for example, PyObject_CallFunctionObjArgs(func, NULL)
allocates 960 bytes on the stack per call, whereas
PyObject_CallNoArgs(func) only allocates 624 bytes per call.

It is excluded from stable ABI 3.8.

Replace private _PyObject_CallNoArg() with public
PyObject_CallNoArgs() in C extensions: _asyncio, _datetime,
_elementtree, _pickle, _tkinter and readline.

Remove _dummy_thread and dummy_threading modules. These modules
were deprecated since Python 3.7 which requires threading support.

bpo-35031, bpo-35998: Reintroduce workaround on Windows and FreeBSD
in test_start_tls_server_1() of test_asyncio: disable TLS v1.3 on the
client context.

On Windows, os.dup() no longer creates an inheritable fd when handling a
character file.

The patch needed for 2.7 should make the test more stable on 3.x also.