__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.
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__().
This allows generators that are using yield from to be seen by debuggers. It
also kills the f_yieldfrom field on frame objects.
Patch mostly from Mark Shannon with a few tweaks by me.
