Goals for Python 3.5

Python 3.4 is in its first beta and the release is just around the corner.  Hurray!  That means we are in feature freeze.  While I am finishing up odds and ends for the PEP 451 (module specs) implementation, I'm also starting to think seriously about what I hope to accomplish for the next Python version, 3.5.

The following are lists of things I'd like to make happen for Python 3.5.  Most of them are things I wanted to do for 3.4 but ran out of time (go figure).  I'll be adding to this list as I run across things I missed.  I'm sure I've missed a thing or three that I promised myself or someone else that I'd work on.

Inspired in part by Nick Coghlan, I've categorized this 3.5 wishlist in descending order of likelihood.

[WARNING: Realistically, a bunch of this will not happen.]

Must-haves

These things are my main priorities.  Barring rejection in python-dev, I will work to push these through.

1. a C implementation of OrderedDict (basically done)
2. OrderedDict as the default class definition namespace [guido]
3. a __definition_order__ attribute on classes that preserves the order of keys (or at least the keys) [me]
4. a __kwargs_order__ attribute in function locals that preserves the order of keys from **kwargs in calls (in lieu of making kwargs an OrderedDict) [link]
5. a new type that abstracts the full import system (similar to PEP 406)
    - incl. exposing suffix->loader mapping
    - context manager support
6. add statement local namespaces [PEP 3150][PEP 403][PEP 340][PEP 359][Nick]

#1-4 are all related, though 4 probably won't involve OrderedDict when all is said and done.  They shouldn't require all that much work to take across the finish line.

Helping Out

These are things that I expect others will be targeting for 3.5 and with which I plan on helping.

* refactor pythonrun.c [PEP 432]
* refactor the C extension module API to take advantage of the PEP 451 loader APIs [import-sig link][issue16421][issue13429][issue16392?]
    - incl. implement exec_module() for BuiltinImporter and ExtensionFileLoader
* a successor to PEP 395
* "speed up" interpreter start-up, import [issue16101][link][link]
* [subinterpreters] (incl. using them to circumvent GIL? [link], interpreter-per-thread)
* a pure python zip importer [link]
* a lazy importer [link]
* missing *-unpacking generalizations [PEP 448]
* add --path0/--no-path0 cmdline options (also issue15716)
* add __locallookup__ method to metaclass [PEP 447]?

* address the hacky uses of function parameter defaults [link] (Jan K.)

Smaller Tasks

These are things that I hope to get done for 3.5, but won't require a lot of work.

* a new frame attribute, f_func, which is a weakref to the function object that was actually called (basically done)
* give the sys module a custom type and add descriptors [link]
* add inspect.Signature.from_callable()
* change setup.py (the main one) to not rely on imp.load_dynamic() [imp => _imp?] (may be done already)
* update pickle to use __spec__ (in the __main__ case)

Would be Nice

Stuff that I'd like to see in 3.5 but that I likely won't have time to work on.

* interpreter startup hook (via cmdline option) [link] (for coverage.py, etc.)
* allow classes to be referenced in the class body
* extension/plugin framework for unittest a la nose [link]

May Be a Good Idea...

Other things that may or may not be worth doing.

* expose _SpecMethods (or something like it) publicly
* add importlib.util.load_from_spec()?
* .ref files [link]

* find a non-hacky replacement for a module replacing itself in sys.modules [link]
* re-organize the sys module with sub-namespaces along the lines of the config categories listed in PEP 432 (similar to but more extensive than PEP 3139)

* parser hooks
* tokenizer hooks
* traceback hooks
* API for excluding functions/methods from tracebacks like importlib and unittest do [issue1705520?]

* spec.data (a wrapper for the data-related API of loaders) [issue14982?]

* add a classonlymethod decorator (not necessarily as a builtin) [link]
* support positional-only parameters (via decorator?) [link][PEP 457]
* add a listproxy type to parallel dictproxy?
* improve re-import of builtin modules, extension modules (see above in Helping Out) [issue14715?]
* generic context API (incl. Context, ThreadLocalContext), a la decimal (email policy?) (asyncio concerns [link])
* post-import hooks (a la PEP 369)
* abc.implements(obj, *<ABC>) that ensures the object has all the appropriate attributes
* ABCMeta.implements(decorated) that registers the decorated class on an ABC and wraps the decorated class's __init__() with an abc.implements() call after it runs [issue12128]
* some mechanism to inherit docstrings [issue15582][issue15731]
* expose PyArg_ParseTuple, etc. in Python
* function to resolve __qualname__ (or provide func.__origin__)

More Radical Ideas

* always import from <module.py> and set __path__ if there is a directory by the same name (obviates __init__.py) [link] (related to PEP 402 discussions) -- at least provide an import hook
* provide a safe mode for ImportSystem (see #5 above) that prevents leaking import side effects outside a context

* replace "if __name__ == '__main__'" [link][PEP 299][PEP 3122] (__spec__.is_main + builtin is_main?)

* a reverse name binding protocol (the object being bound/unbound to the name is notified) [link]

* expose key metaclass operations via special class methods (a la PEP 422)
* attribute docstrings [link]
* a hook to process a docstring after its corresponding object is created (but before decorators are applied)

* revisit PEP 224, PEP 329, PEP 351, PEP 363, PEP 377 (Kristjan)

Random Off-the-cuff Ideas

* a decorator for type hints (optional static typing)
* a decorator that supports all sorts of *args/**kwargs handling
* define a standard API for object (modules included) to "install" themselves; provide installer helpers (a la install_importhook() or an Installer base class + ImportHookInstaller base subclass)
* generic Registry class (register() method, etc.)
* spec.open() for locatable specs
* expose an easy way to make some module-global read-only (make use of loader.create_module()?) [issue15031]
* break or return in global module code to stop early (instead of delegating skipped code to submodule)
* ...

This list is as endless as the sea! :-)