* Make sure ``__spec__.loader`` matches ``__loader__`` for namespace packages.
* Make sure ``__spec__.origin` matches ``__file__`` for namespace packages.

https://bugs.python.org/issue32303
https://bugs.python.org/issue32305

BytesWarning no longer emitted when the fromlist argument of
__import__() or the __all__ attribute of the module contain bytes
instances.

* Trivial cleanups following bpo-31370

* Also cleanup the "importlib._bootstrap_external" module

Use sys.modules.get() in the "with _ModuleLockManager(name):" block
to protect the dictionary key with the module lock and use an atomic
get to prevent race condition.

Remove also _bootstrap._POPULATE since it was unused
(_bootstrap_external now has its own _POPULATE object), add a new
_SENTINEL object instead.

instead of failing with SystemError.

Relative import from non-package now fails with ImportError rather than
SystemError.

* Rewrite importlib _get_module_lock(): it is now responsible to hold
  the imp lock directly.
* _find_and_load() now holds the module lock to check if name is in
  sys.modules to prevent a race condition

PEP 432 specifies a number of large changes to interpreter startup code, including exposing a cleaner C-API. The major changes depend on a number of smaller changes. This patch includes all those smaller changes.

Class was dead code. Thanks to Xiang Zhang for the patch.

Thanks to Oren Milman for the patch.

Most fixes to Doc/ and Lib/ directories by Ville Skyttä.

Issue #26637: The importlib module now emits an ImportError rather than a
TypeError if __import__() is tried during the Python shutdown process but
sys.path is already cleared (set to None).

'level' is specified but no __package__.

This brings the function inline with builtins.__import__(). Thanks to
Manuel Jacob for the patch.

In a previous change, __spec__.parent was prioritized over
__package__. That is a backwards-compatibility break, but we do
eventually want __spec__ to be the ground truth for module details. So
this change reverts the change in semantics and instead raises an
ImportWarning when __package__ != __spec__.parent to give people time
to adjust to using spec objects.

not defined for a relative import.

This is the start of work to try and clean up import semantics to rely
more on a module's spec than on the myriad attributes that get set on
a module. Thanks to Rose Ames for the patch.

longer formatted twice.

is disabled.  Patch by Petr Viktorin.

Known limitations of the current implementation:

- documentation changes are incomplete
- there's a reference leak I haven't tracked down yet

The leak is most visible by running:

  ./python -m test -R3:3 test_importlib

However, you can also see it by running:

  ./python -X showrefcount

Importing the array or _testmultiphase modules, and
then deleting them from both sys.modules and the local
namespace shows significant increases in the total
number of active references each cycle. By contrast,
with _testcapi (which continues to use single-phase
initialisation) the global refcounts stabilise after
a couple of cycles.

The concept of .pyo files no longer exists. Now .pyc files have an
optional `opt-` tag which specifies if any extra optimizations beyond
the peepholer were applied.

importlib.abc.Loader.exec_module() is also defined.

Before this change, create_module() was optional **and** could return
None to trigger default semantics. This change now reduces the
options for choosing default semantics to one and in the most
backporting-friendly way (define create_module() to return None).

  asked to compile a source file containing multiple dots in the source file
  name.

working directory no longer exists.

Thanks to Martin Panter for the bug report.

sys.path_hooks when set to None during interpreter shutdown.

Thanks to Martin Panter for the initial bug report.

Along the way, dismantle importlib._bootstrap._SpecMethods as it was
no longer relevant and constructing the new function required
partially dismantling the class anyway.

PathEntryFinder instances which only define find_module().

Reported by Yukihiro Nakadaira.

PathEntryFinder instances which only define find_module().

Reported by Yukihiro Nakadaira.

This code was an artifact of issuing a DeprecationWarning for the lack
of loader.exec_module().  However, we have deferred such warnings to
later Python versions.