Summary of changes:
1. Coroutines now have a distinct, separate from generators
type at the C level: PyGen_Type, and a new typedef PyCoroObject.
PyCoroObject shares the initial segment of struct layout with
PyGenObject, making it possible to reuse existing generators
machinery. The new type is exposed as 'types.CoroutineType'.
As a consequence of having a new type, CO_GENERATOR flag is
no longer applied to coroutines.
2. Having a separate type for coroutines made it possible to add
an __await__ method to the type. Although it is not used by the
interpreter (see details on that below), it makes coroutines
naturally (without using __instancecheck__) conform to
collections.abc.Coroutine and collections.abc.Awaitable ABCs.
[The __instancecheck__ is still used for generator-based
coroutines, as we don't want to add __await__ for generators.]
3. Add new opcode: GET_YIELD_FROM_ITER. The opcode is needed to
allow passing native coroutines to the YIELD_FROM opcode.
Before this change, 'yield from o' expression was compiled to:
(o)
GET_ITER
LOAD_CONST
YIELD_FROM
Now, we use GET_YIELD_FROM_ITER instead of GET_ITER.
The reason for adding a new opcode is that GET_ITER is used
in some contexts (such as 'for .. in' loops) where passing
a coroutine object is invalid.
4. Add two new introspection functions to the inspec module:
getcoroutinestate(c) and getcoroutinelocals(c).
5. inspect.iscoroutine(o) is updated to test if 'o' is a native
coroutine object. Before this commit it used abc.Coroutine,
and it was requested to update inspect.isgenerator(o) to use
abc.Generator; it was decided, however, that inspect functions
should really be tailored for checking for native types.
6. sys.set_coroutine_wrapper(w) API is updated to work with only
native coroutines. Since types.coroutine decorator supports
any type of callables now, it would be confusing that it does
not work for all types of coroutines.
7. Exceptions logic in generators C implementation was updated
to raise clearer messages for coroutines:
Before: TypeError("generator raised StopIteration")
After: TypeError("coroutine raised StopIteration")
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).
Along the way, dismantle importlib._bootstrap._SpecMethods as it was
no longer relevant and constructing the new function required
partially dismantling the class anyway.
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.
old methods now provide implementations when PEP 451 APIs are present.
This should help with backwards-compatibility with code which has not
been updated to work with PEP 451.
Early in the PEP 451 implementation some of the importlib loaders had
their own _get_spec() methods to simplify accommodating them. However,
later implementations removed the need. They simply failed to remove
this code at the same time. :)
module loaders.
Due to the fact that the call signatures for extension modules and
built-in modules does not allow for the specifying of what module to
initialize and that on Windows all extension modules are built-in
modules, work to clean up built-in and extension module initialization
will have to wait until Python 3.5. Because of this the semantics of
exec_module() would be incorrect, so removing the methods for now is
the best option; load_module() is still used as a fallback by
importlib and so this won't affect semantics.
importlib.machinery.FileFinder.
While originally moved to stop special-casing '' as PathFinder farther
up the typical call chain now uses the cwd in the instance of '', it
was deemed an unnecessary risk to breaking subclasses of FileFinder to
take the special-casing out.
exists when checking for a package.
Before there was an isdir check and then various isfile checks for
possible __init__ files when looking for a package.
This change drops the isdir check by leaning
on the assumption that a directory will not contain something named
after the module being imported which is not a directory. If the module
is a package then it saves a stat call. If there is nothing in the
directory with the potential package name it also saves a stat call.
Only if there is something in the directory named the same thing as
the potential package will the number of stat calls increase
(due to more wasteful __init__ checks).
Semantically there is no change as the isdir check moved
down so that namespace packages continue to have no chance of
accidentally collecting non-existent directories.
