__loader__.

Since import now sets __loader__ on all modules it creates and
imp.reload() already relied on the attribute for modules that import
didn't create, the only potential compatibility issue is if people
were deleting the attribute on modules and expecting imp.reload() to
continue to work.

rewriting functionality in pure Python.

To start, imp.new_module() has been rewritten in pure Python, put into
importlib (privately) and then publicly exposed in imp.

of sys.modules when possible.

This is being done for two reasons. One is to gain a little bit of
performance by skipping an unnecessary dict lookup in sys.modules. But
the other (and main) reason is to be a little bit more clear in how
things should work from the perspective of import's interactions with
loaders. Otherwise loaders can easily forget to return the module even
though PEP 302 explicitly states they are expected to return the module
they loaded.

found in sys.modules.

Issue #13889: On MSVC builds, set FPU control word at runtime for all string <-> float conversions.  Patch by Samuel Iseli and Stefan Krah.

_socket does.  Some were using the older wsock32.lib.

PEP 328 in explaining how 'index' works.

__import__('mod', {'__packaging__': 'pkg', level=1) w/o properly (and
thus not segfaulting).

Python 3.3 thanks to importlib finishing the work in PEP 328 that
accidently got carried forward.

importlib._bootstrap is now frozen into Python/importlib.h and stored
as _frozen_importlib in sys.modules. Py_Initialize() loads the frozen
code along with sys and imp and then uses _frozen_importlib._install()
to set builtins.__import__() w/ _frozen_importlib.__import__().