[Python] Cannot create pointer type for a Structure subclass within __init_subclass__ using...

import ctypes
from ctypes.wintypes import *

class xStructure(ctypes.Structure):
def __init_subclass__(cls):
p = ctypes.POINTER(cls)

class OFFSET_VAL_II_C4(xStructure):
_fields_ = [('ValOrig', DOUBLE),
('MaxChangeVal', DOUBLE),
('ActChangeVal', DOUBLE)]


The code above results in TypeError: _type_ must have storage info triggered by line 6 (p = ctypes.POINTER(cls)).

However, the code below works just fine.

import ctypes
from ctypes.wintypes import *

class xStructure(ctypes.Structure):
pass

class OFFSET_VAL_II_C4(xStructure):
_fields_ = [('ValOrig', DOUBLE),
('MaxChangeVal', DOUBLE),
('ActChangeVal', DOUBLE)]

p = ctypes.POINTER(OFFSET_VAL_II_C4)


My researches into the specific TypeError suggested it is caused by an attempt to create a pointer type for something that is not a ctype. However, in this case, OFFSET_VAL_II_C4 is a subclass of ctypes.Structure (via xStructure), so should work - and does, as evidenced by the second example.

What am I missing?

(For those wondering why I want to do this, there is a reason that I am happy to elaborate, but I am well aware that the minimal code here is utterly pointless!)

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