Initial patch by Chandan Kumar.

path_error() uses GetLastError() on Windows, but some os functions
are implemented via CRT APIs which report errors via errno.
This may result in raising OSError with invalid error code (such
as zero).

Introduce posix_path_error() function and use it where appropriate.

If buffering=1 is specified for open() in binary mode, it is silently
treated as buffering=-1 (i.e., the default buffer size).
Coupled with the fact that line buffering is always supported in Python 2,
such behavior caused several issues (e.g., bpo-10344, bpo-21332).

Warn that line buffering is not supported if open() is called with
binary mode and buffering=1.

sys and threading were imported twice.

The docs in `library/unittest.mock` have been updated to remove
confusing terms about submock and be explicit about the behavior
expected.

* Simplify the C code.
* Simplify tests and make them more strict and robust.
* Add references in the documentation.

The reprlib code was copied here instead of importing reprlib. I'm not sure if we really need to avoid the import, but since I expect dataclasses to be more common that reprlib, it seems wise. Plus, the code is small.

Use tp_members and tp_getset instead.

for invalid escape sequences in string and bytes literals.

Adding `max_num_fields` to `cgi.FieldStorage` to make DOS attacks harder by
limiting the number of `MiniFieldStorage` objects created by `FieldStorage`.

It is now guarantied that children of xml.etree.ElementTree.Element
are Elements (at least in C implementation). Previously methods
__setitem__(), __setstate__() and __deepcopy__() could be used for
adding non-Element children.

This allows *from_* to be successfully set to a non-default value when calling mbox.get_string.

This is intended to help code explorers find out more about what's defined there.

Update the outdated install-sh file to the latest
revision from automake v1.16.1

C implementation of xml.etree.ElementTree.Element.__setstate__()
leaked references to children when called for already initialized
element.

Restores the use of pyexpatns.h to isolate our embedded copy of the expat C
library so that its symbols do not conflict at link or dynamic loading time
with an embedding application or other extension modules with their own
version of libexpat.

https://github.com/python/cpython/commit/5dc3f23b5fb0b510926012cb3732dae63cddea60#diff-3afaf7274c90ce1b7405f75ad825f545 inadvertently removed it when upgrading expat.

 On macOS, fix reading from and writing into a file with a size larger than 2 GiB. 

Verify the value for the parameter '-s' of the cProfile CLI. Patch by Robert
Kuska.
Co-authored-by: Robert Kuska <rkuska@gmail.com>

According to the versionchanged note, the `strict` argument was removed in 3.3 and `policy` was added, but the name of the argument in the paragraph wasn't updated.

When runnint test_logging with --huntrleaks after commit
18fb1fb9, test_out_of_order fails
to raise ValueError due to the fact that the new test
test_out_of_order_with_dollar_style mutates the out_of_order
dictionary. Even if the test copies the dictionary first, the mutation
is done in a very deep level so the original one is also affected.

Fix test_cmd_line_script.test_nonexisting_script(): the test must not
rely on sys.executable, since main.c uses config->program which can
be different than sys.executable in many cases (for example, on macOS
when using the framework).

bpo-23554: Change echo server example class name from EchoServerClientProtocol to EchoServerProtocol (GH-9859)