cc @vstinner @ericsnowcurrently

Thanks for reporting this! If I knew about this earlier I'd try to make your life easier, but at this point it looks like a docs change is the best way to go.

I'm afraid that by using type(c_void_p) to get to ctypes.PyCSimpleType internals, and by importing _pointer_type_cache, you're getting in the realm of things that can change.
Unfortunately, ctypes has been... stable? neglected? ... for a long time, and these workarounds are common in the wild.
If you can, please do plan to test with 3.14 as the alphas/betas come out, and ping me on any other incompatibilities you might find.

For the diff you linked:

Unfortunately I don't have a Windows box to test on. What error are you getting if you put all of the logic in __init__? (Is it __init__() should return None? Don't return self from __init__.)

If the if/else is needed, I recommend putting the logic in common methods like _new and _init to remove the duplication, so the branch becomes something like:

if sys.version_info >= (3, 13):
    def __new__(cls, ...):
       return cls._new(...)
    def __init__(self, ...):
       self._init(...)
else:
    def __new__(cls, ...):
       self = cls._new(cls, ...)
       self.__init__(...)
       return self

or even:

if sys.version_info >= (3, 13):
    __new__ = _new
    __init__ = _init
else:
    def __new__(cls, ...):
       self = cls._new(cls, ...)
       self._init(...)
       return self

It is necessary to pass arguments directly to the metaclass instead of using new in places where the metaclass is instantiated (i.e., where the class is dynamically defined).

Hm, I don't understand this point. Do you have an example?

It is necessary to pass arguments directly to the metaclass instead of using new in places where the metaclass is instantiated (i.e., where the class is dynamically defined).

Hm, I don't understand this point. Do you have an example?

In comtypes, the following part corresponds to this.

https://github.com/enthought/comtypes/compare/c631f97..6f036d4

    meta = type(_safearray.tagSAFEARRAY)
-   sa_type = meta.__new__(
-       meta, "SAFEARRAY_%s" % itemtype.__name__, (_safearray.tagSAFEARRAY,), {}
-   )
+   sa_type = meta(f"SAFEARRAY_{itemtype.__name__}", (_safearray.tagSAFEARRAY,), {})

enthought/comtypes#618 (comment)

Unfortunately I don't have a Windows box to test on. What error are you getting if you put all of the logic in __init__?

--- a/comtypes/_post_coinit/unknwn.py
+++ b/comtypes/_post_coinit/unknwn.py
@@ -75,7 +75,9 @@ class _cominterface_meta(type):
             new_cls._methods_ = methods
         if dispmethods is not None:
             new_cls._disp_methods_ = dispmethods
+        return new_cls

+    def __init__(self, name, bases, namespace):
         # If we sublass a COM interface, for example:
         #
         # class IDispatch(IUnknown):
@@ -85,23 +87,22 @@ class _cominterface_meta(type):
         # subclass of POINTER(IUnknown) because of the way ctypes
         # typechecks work.
         if bases == (object,):
-            _ptr_bases = (new_cls, _compointer_base)
+            _ptr_bases = (self, _compointer_base)
         else:
-            _ptr_bases = (new_cls, POINTER(bases[0]))
+            _ptr_bases = (self, POINTER(bases[0]))

         # The interface 'new_cls' is used as a mixin.
         p = type(_compointer_base)(
-            "POINTER(%s)" % new_cls.__name__,
+            "POINTER(%s)" % self.__name__,
             _ptr_bases,
-            {"__com_interface__": new_cls, "_needs_com_addref_": None},
+            {"__com_interface__": self, "_needs_com_addref_": None},
         )

         from ctypes import _pointer_type_cache

-        _pointer_type_cache[new_cls] = p
-
-        if new_cls._case_insensitive_:
+        _pointer_type_cache[self] = p

+        if self._case_insensitive_:
             @patcher.Patch(p)
             class CaseInsensitive(object):
                 # case insensitive attributes for COM methods and properties
@@ -155,8 +156,6 @@ class _cominterface_meta(type):

                 CopyComPointer(value, self)

-        return new_cls
-

The following error occurs in Python 3.11 when making the changes mentioned above.

Traceback (most recent call last):
  File "...\Python311\Lib\unittest\__main__.py", line 18, in <module>
    main(module=None)
  File "...\Python311\Lib\unittest\main.py", line 101, in __init__
    self.parseArgs(argv)
  File "...\Python311\Lib\unittest\main.py", line 150, in parseArgs
    self.createTests()
  File "...\Python311\Lib\unittest\main.py", line 161, in createTests
    self.test = self.testLoader.loadTestsFromNames(self.testNames,
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "...\Python311\Lib\unittest\loader.py", line 220, in loadTestsFromNames
    suites = [self.loadTestsFromName(name, module) for name in names]
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "...\Python311\Lib\unittest\loader.py", line 220, in <listcomp>
    suites = [self.loadTestsFromName(name, module) for name in names]
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "...\Python311\Lib\unittest\loader.py", line 154, in loadTestsFromName
    module = __import__(module_name)
             ^^^^^^^^^^^^^^^^^^^^^^^
    from comtypes._post_coinit import _shutdown
  File "...\comtypes\_post_coinit\__init__.py", line 15, in <module>
    from comtypes._post_coinit.unknwn import _shutdown  # noqa
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "...\comtypes\_post_coinit\unknwn.py", line 370, in <module>
    class _compointer_base(c_void_p, metaclass=_compointer_meta):
  File "...\comtypes\_post_coinit\unknwn.py", line 95, in __init__
    p = type(_compointer_base)(
             ^^^^^^^^^^^^^^^^
NameError: name '_compointer_base' is not defined. Did you mean: '_compointer_meta'?

Thanks!
I won't be able to debug that by reading the code. I'll follow up next week when I get back to a Windows PC.

Thank you.

If I knew about this earlier I'd try to make your life easier, but at this point it looks like a docs change is the best way to go.

Fortunately, libraries like comtypes and pyglet were able to adapt with changes to the codebase.
However, if there is a codebase that performs more complex pre-processing before calling super().__new__ within __new__, it might need more complex workarounds.

If it is still possible to modify things so that performing all initialization in __new__ does not result in an error, that would be great.
Alternatively, documenting a workaround for such cases would be helpful for maintainers of those kinds of packages.