Implement PEP 649 and PEP 749

[JelleZijlstra]

PEP-649 has been accepted and should be implemented in Python 3.14. Let's use this issue to track the implementation:

• Decide on or clarify the adoption strategy (https://discuss.python.org/t/pep-649-deferred-evaluation-of-annotations-tentatively-accepted/21331/44)
• Add new __annotate__ attributes gh-119180: PEP 649: Add __annotate__ attributes #119209
• Implement core interpreter changes (e.g., new symbol table functionality) gh-119180: PEP 649 compiler changes #119361
• Implement new Python-level APIs, like the new format argument to inspect.get_annotations gh-119180: Add annotationlib module to support PEP 649 #119891
  • (PEP-649 specifies that inspect.AnnotationsFormat should be a "global enum". Is that desirable? TBD. https://github.com/python/cpython/pull/119361/files#r1614753031)
• Document the new semantics gh-119180: Documentation for PEP 649 and 749 #122235
  • Add higher-level documentation, e.g. a migration guide away from from __future__ import annotations; an introduction to annotationlib; an update to Larry's annotations HOWTO
  • The SC would like https://peps.python.org/pep-0749/#appendix incorporated into the docs
• Make staticmethod and classmethod not force evaluation of annotations gh-119180: Lazily wrap annotations on classmethod and staticmethod #119864
• Adapt standard library code that uses annotations to work excellently with PEP 649
  • dataclasses gh-119180: Add annotationlib module to support PEP 649 #119891
  • typing.py: TypedDict, NamedTuple, try to remove dependency on inspect. (If it can't be removed, get rid of the awkward dance we do for typing.Protocol to import inspect.getattr_static lazily.)
  • singledispatch gh-119180: Add annotationlib module to support PEP 649 #119891
    • Also make it only evaluate the relevant parameter, gh-119180: Add annotationlib module to support PEP 649 #119891 (comment)
  • functools.update_wrapper gh-119180: Add annotationlib module to support PEP 649 #119891, PEP 649: functools.update_wrapper implementation #124342
• Add PEP 649-like functionality to TypeAliasType, TypeVar, etc. (pep649-typevar branch in my fork)
• Make sure the ecosystem is ready by testing third-party libraries like Pydantic
  • typing_extensions: needs changes similar to those in typing.py (Support my PEP 649 branch typing_extensions#412)
  • beartype: had various unrelated problems on 3.13 ([Future] Python 3.13 conformance beartype/beartype#387); a few additional tests fail on the PR branch due to direct manipulation of __dict__
  • typeguard: some unrelated 3.13 problems (Support Python 3.13 agronholm/typeguard#460); no test failures related to PEP 649
  • pyanalyze: some unrelated 3.13 issues and a few changes necessary due to direct __dict__ access (Support Python 3.13 quora/pyanalyze#773)
  • pydantic: failed to build for 3.14 so far
• Optimize the implementation. Ideas:
  • Avoid creation of function objects and store only code objects instead PEP 649: Avoid creation of function objects for __annotate__ #124157
  • Avoid creation of AST nodes and use of eval() for ForwardRefs that are just names gh-119180: Avoid going through AST and eval() when possible in annotationlib #124337

Things to revisit:

• Should FORWARDREF be the default? Some improvements for Python 3.14 / PEP 649 support beartype/beartype#440 (comment)
• Add VALUE_WITH_FAKE_GLOBALS format
• Name of __annotate__ parameter
• Should setting __annotations__ invalidate __annotate__?
• Rename SOURCE to STRING?

I am planning to work on the interpreter core first.

cc @larryhastings @carljm @samuelcolvin

Linked PRs

• gh-119180: PEP 649: Add __annotate__ attributes #119209
• gh-119180: Add LOAD_COMMON_CONSTANT opcode #119321
• gh-119180: PEP 649 compiler changes #119361
• gh-119180: Update the magic number #119397
• gh-119180: Lazily wrap annotations on classmethod and staticmethod #119864
• gh-119180: Add annotationlib module to support PEP 649 #119891
• gh-119180: Fix annotations lookup on classes with custom metaclasses #120719
• gh-119180: Alternative approach to metaclass annotations: never use the dict #120816
• gh-119180: Use type descriptors to access annotations (PEP 749) #122074
• gh-119180: Improvements to ForwardRef.evaluate #122210
• gh-119180: Add evaluate functions for type params and type aliases #122212
• gh-119180: Documentation for PEP 649 and 749 #122235
• gh-119180: annotationlib: Fix __all__, other minor fixes #122365
• gh-119180: Add myself as CODEOWNER for annotationlib #122366
• gh-119180: Fix annotationlib.ForwardRef.evaluate with no globals #124326
• gh-119180: Avoid going through AST and eval() when possible in annotationlib #124337
• gh-119180: Add discussion of annotations to the 3.14 What's New #124393
• gh-119180: Add VALUE_WITH_FAKE_GLOBALS format to annotationlib #124415
• gh-119180: Rename parameter to __annotate__ functions #124461
• gh-119180: Make FORWARDREF format look at __annotations__ first #124479
• gh-119180: Disallow instantiation of ConstEvaluator objects #124561
• gh-119180: Rename SOURCE format to STRING #124620
• gh-119180: No longer set __annotations__ in __main__ #124634
• gh-119180: Set the name of the param to __annotate__ to "format" #124730
• gh-119180: Use equality when comparing against annotationlib.Format #131755
• gh-119180: Make the FORWARDREF format work with more kinds of runtime errors #133407
• gh-119180: More documentation for PEP 649/749 #133552
• gh-119180: annotationlib: Fix values of Format members in docs #133841
• [3.14] gh-119180: More documentation for PEP 649/749 (GH-133552) #133902
• [3.14] gh-119180: annotationlib: Fix values of Format members in docs (GH-133841) #133903