Patch by Serhiy Storchaka.

Patch by Serhiy Storchaka.

Close #15486: Simplify the mechanism used to remove importlib frames from tracebacks when they just introduce irrelevant noise

Lib/imp.py for imp.source_from_cache() instead of its own C version.

Also change PyImport_ExecCodeModuleObject() to not infer the source
path from the bytecode path like
PyImport_ExecCodeModuleWithPathnames() does. This makes the function
less magical.

This also has the side-effect of removing all uses of MAXPATHLEN in
Python/import.c which can cause failures on really long filenames.

Lib/imp.py.

defined in sysmodule.c instead of straight out of a Unicode object.

Thanks to Amaury Forgeot d'Arc for noticing the bug and Eric Snow for
writing the patch.

Also eliminates some C code in Python/import.c as well.

Patch by Eric Snow with verification by comparing against another
patch from Jeff Knupp.

Py_UCS4 buffer

Close #14857: fix regression in references to PEP 3135 implicit __class__ closure variable. Reopens issue #12370, but also updates unittest.mock to workaround that issue

Most of the import sequence now uses per-module locks rather than the
global import lock, eliminating well-known issues with threads and imports.

Issue #14583: Fix importlib bug when a package's __init__.py would first import one of its modules then raise an error.

This introduces a new function, imp.extension_suffixes(), which is
currently undocumented. That is forthcoming once issue #14657 is
resolved and how to expose file suffixes is decided.

Thanks to Eric Snow for the patch.

finder instead of using some (now non-existent) implicit finder.

 * In debug mode, fill the string data with invalid characters
 * Simplify also reference counting in PyCodec_BackslashReplaceErrors()
   and PyCodec_XMLCharRefReplaceError()

Thanks to Eric Snow for taking an initial stab at the implementation.