Open issue: typing_objects function definitions

[Viicos]

Currently, typing-inspection works on the supported Python versions (3.9-3.14) and has a lower bound on typing-extensions:

typing-inspection/pyproject.toml

Lines 31 to 33 in 168c1e4

	dependencies = [
	'typing-extensions>=4.12.0',
	]

Version 4.12.0 was released almost a year ago, so it seemed reasonable to choose it as a lower bound. In the future, it would be great if typing-extensions could keep this lower bound as long as possible. This means that the typing_objects inspection functions need to handle several different cases. For a typing member TypingObj:

• Both typing.TypingObj and typing_extensions.TypingObj exist.
  • typing_extensions is simply reexporting typing.TypingObj, in this case, typing_objects.is_typingobj() can be implemented as:

    def is_typingobj(obj, /) -> bool:
        return obj is typing.TypingObj

  • typing_extensions backports a different version of TypingObj. In this case, the check can be implemented as:

    def is_typingobj(obj, /) -> bool:
        return obj is typing.TypingObj or obj is typing_extensions.TypingObj

• Only typing_extensions.TypingObj exists (e.g. when not on the latest Python version):

  def is_typingobj(obj, /) -> bool:
       return obj is typing_extensions.TypingObj

• Only typing.TypingObj exists (e.g. when not on the latest typing_extensions version):

  def is_typingobj(obj, /) -> bool:
       return obj is typing.TypingObj

• TypingObj doesn't exist in both modules:

  def is_typingobj(obj, /) -> bool:
       return False

Several options are offered to us to implement the checks:

• At the module level, use hasattr()/sys.version_info checks to define the functions. This can get repetitive and unreadable very quickly.
• At the module level, define a set containing the members to check against:

  _typingobj_members = {}
  if hasattr(typing, 'TypingObj'):
      _typingobj_members.add(typing.TypingObj)
  if hasattr(typing_extensions, 'TypingObj'):
      _typingobj_members.add(typing_extensions.TypingObj)
  
  def is_typingobj(obj, /) -> bool:
      return obj in _typingobj_members

  A bit less repetitive.
• Do the hasattr()/sys.version_info checks in the function. This could degrade performance slightly (in Pydantic, we rely a lot on thes introspection functions, and noticed small performance improvements (~1-5%) when optimizing them).
• Dynamically create the functions. This is what _compile_identity_check_function()/_compile_isinstance_check_function() are currently doing.

The chosen approach works fine, but requires generating typing stubs, and conceptually feels a bit hacky (functions are generated using exec()). I'm open to suggestions that would provide a cleaner implementation without hurting performance.