Self issue with PySide (fix proposal)

[noamgot]

Hello
While the issue I describe is a very weird phenomenon that's not directly related to typing_extensions, I would like to propose a solution that might be able to solve this.

Note: this is an issue related to python <=3.10

Minimal reproducable example

import typing

print(hasattr(typing, "Self"))

import PySide6 # noqa

print(hasattr(typing, "Self"))

This prints:

False
True

In other words, PySide6 manipulates python's built-in typing module.

Observation

Examining typing_extension.py, I found this section

typing_extensions/src/typing_extensions.py

Lines 2277 to 2281 in 59d2c20

	if hasattr(typing, "Self"): # 3.11+
	Self = typing.Self
	else:
	@_SpecialForm
	def Self(self, params):

Proposal

Would it make sense to check sys.version_info instead of checking the existance of Self attribute?
This is already done in several places, e.g.:

typing_extensions/src/typing_extensions.py

Lines 192 to 196 in 59d2c20

	if sys.version_info >= (3, 11):
	from typing import Any
	else:
	class _AnyMeta(type):

IMHO it looks like a more robust solution (that can solve this specific problem)

I would love to hear your thoughts. I'd be happy to open a PR if needed.

Thanks!

[JelleZijlstra]

We use the version approach in cases where the symbol exists in typing, but with some different behavior than what we want. (In the case you cited, Any, it's that on older versions Any existed, but couldn't be subclassed from; typing_extensions.Any allows subclassing on all versions.)

I don't know what PySide6 is doing or why, but this seems more like something that should be fixed in that package, not here. What concrete problem is the current code in typing-extensions causing you?

[noamgot]

I get an error when trying to import from the cloudpathlib library:

Traceback (most recent call last):
  File ".../lib/python3.10/runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File ".../lib/python3.10/runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File ".../reports/gui/main.py", line 95, in <module>
    from reports.gui.startup import run_gui
  File ".../reports/gui/startup.py", line 3, in <module>
    from cloudpathlib import AnyPath
  File ".../site-packages/cloudpathlib/__init__.py", line 3, in <module>
    from .anypath import AnyPath
  File ".../site-packages/cloudpathlib/anypath.py", line 6, in <module>
    from .cloudpath import InvalidPrefixError, CloudPath
  File ".../site-packages/cloudpathlib/cloudpath.py", line 181, in <module>
    class CloudPath(metaclass=CloudPathMeta):
  File ".../site-packages/cloudpathlib/cloudpath.py", line 201, in CloudPath
    cloud_path: Union[str, Self],
  File ".../lib/python3.10/typing.py", line 312, in inner
    return func(*args, **kwds)
  File ".../lib/python3.10/typing.py", line 403, in __getitem__
    return self._getitem(self, parameters)
  File ".../lib/python3.10/typing.py", line 515, in Union
    parameters = tuple(_type_check(p, msg) for p in parameters)
  File ".../lib/python3.10/typing.py", line 515, in <genexpr>
    parameters = tuple(_type_check(p, msg) for p in parameters)
  File ".../lib/python3.10/typing.py", line 171, in _type_check
    raise TypeError(f"Plain {arg} is not valid as type argument")
TypeError: Plain typing.Self is not valid as type argument

By the way, switching the import order solves this issue (importing PySide6 after cloudpathlib).
You are correct that it makes more sense to fix it there, but I thought my approach made sense (I understand what you said about the differences between this approach and the current one that's used for Self).