ctypes: subclassed swapped endianness doesn't swap

Bug report

Subclassing a swapped simple type and calling from_buffer_copy doesn't swap bytes. Here is a minimal non-working example.

import ctypes

cshort_be = ctypes.c_ushort.__ctype_be__
class Short(cshort_be):
    pass

print(cshort_be.from_buffer_copy(b"\x00\x01").value) # prints 1
print(Short.from_buffer_copy(b"\x00\x01").value) # prints 256

However, there is a simple workaround:

print(Short.__ctype_be__.from_buffer_copy(b"\x00\x01").value) # prints 1

I am not sure what happens, but ctypes behave kinda weird when subclassing native types. So this bug might be related to issue #73456.

My environment

• CPython versions tested on: 3.10.5
• Operating system and architecture: Linux Celap 5.18.0-1-amd64 #1 SMP PREEMPT_DYNAMIC Debian 5.18.2-1 (2022-06-06) x86_64 GNU/Linux

Start by reproducing the minimal ctypes example using c_ushort.ctype_be and a subclass, then compare the from_buffer_copy behavior of the base swapped type and subclass. Trace the ctypes handling of swapped simple types and determine how the subclass path differs; done means the subclass produces the same byte-swapped value as the base type and the regression is covered by a test.