ImportError.

The exception is raised by import when a module could not be found.
Technically this is defined as no viable loader could be found for the
specified module. This includes ``from ... import`` statements so that
the module usage is consistent for all situations where import
couldn't find what was requested.

This should allow for the common idiom of::

  try:
    import something
  except ImportError:
    pass

to be updated to using ModuleNotFoundError and not accidentally mask
ImportError messages that should propagate (e.g. issues with a
loader).

This work was driven by the fact that the ``from ... import``
statement needed to be able to tell the difference between an
ImportError that simply couldn't find a module (and thus silence the
exception so that ceval can raise it) and an ImportError that
represented an actual problem.

by their HANDLE which is a pointer (and not a long, which is smaller).

This affects pyexpat and _elementtree. PyExpat_CAPI now exposes a new
function - DefaultUnknownEncodingHandler.

Based on a patch by Serhiy Storchaka.

an internal XML encoding is UTF-8 or US-ASCII.

PyObject_CallMethod() now changed to `const char*`.
Based on patches by Jörg Müller and Lars Buitinck.

A patch from Illia Polosukhin.

(Issue #17807: Generators can now be finalized even when they are part of a reference cycle)

(should fix Windows buildbot failures on test_gc)

Note that this is a potentially disruptive change since it may
release some system resources which would otherwise remain
perpetually alive (e.g. database connections kept in thread-local
storage).

Issue #17408: Avoid using an obsolete instance of the copyreg module when the interpreter is shutdown and then started again.

 * Add also min_char attribute to _PyUnicodeWriter structure (currently unused)
 * _PyUnicodeWriter_Init() has no more argument (except the writer itself):
   min_length and overallocate must be set explicitly
 * In error handlers, only enable overallocation if the replacement string
   is longer than 1 character
 * CJK decoders don't use overallocation anymore
 * Set min_length, instead of preallocating memory using
   _PyUnicodeWriter_Prepare(), in many decoders
 * _PyUnicode_DecodeUnicodeInternal() checks for integer overflow

the legacy Py_UNICODE API.

Add also a new _PyUnicodeWriter_WriteChar() function.

Write a function to enable more optimizations:

 * If the substring is the whole string and overallocation is disabled, just
   keep a reference to the string, don't copy characters
 * Avoid a call to the expensive _PyUnicode_FindMaxChar() function when
   possible

  in marshal

when it needs support from timemodule (which is a .so on linux):
link in timemodule.c for the required functions.

Patch from Sven Brauch.

as reported by Serhiy Storchaka and Matthew Barnett.

Patch by Stefan Behnel and I.